Caddy: Reverse Proxy

Features

Caddy - The Ultimate Server - makes your sites more secure, more reliable, and more scalable than any other solution. By default, Caddy automatically obtains and renews TLS certificates (Let’s Encrypt and ZeroSSL) for all your sites. It’s the most advanced HTTPS server in the world.

WWW: https://caddyserver.com/

All available options and help-texts can be found on Github

Installation

  • Install “os-caddy” from the OPNsense Plugins.

Prepare OPNsense for Caddy After Installation

Attention

Caddy uses port 80 and 443. So the OPNsense WebGUI or other plugins can’t bind to these ports.

Go to System ‣ Settings ‣ Administration

  • Change the TCP Port to 8443 (example), do not forget to adjust the firewall rules to allow access to the WebGUI. On LAN there is a hidden anti-lockout rule that takes care of this automatically. On other interfaces, make sure to add explicit rules.

  • Enable the checkbox for HTTP Redirect - Disable web GUI redirect rule.

Go to Firewall ‣ Rules ‣ WAN

  • Create Firewall rules that allow HTTP and HTTPS to destination This Firewall on WAN

Option

Values

Interface

WAN

TCP/IP Version

IPv4+IPv6

Protocol

TCP

Source

Any

Destination

This Firewall

Destination port range

from: HTTP to: HTTP

Description

Caddy Reverse Proxy HTTP

Option

Values

Interface

WAN

TCP/IP Version

IPv4+IPv6

Protocol

TCP/UDP

Source

Any

Destination

This Firewall

Destination port range

from: HTTPS to: HTTPS

Description

Caddy Reverse Proxy HTTPS

Go to Firewall ‣ Rules ‣ LAN and create the same rules for the LAN interface. Now external and internal clients can connect to Caddy, and Let’s Encrypt or ZeroSSL certificates will be issued automatically. If using a VPN to connect remote clients to the OPNsense, additional firewall rules could be needed.

Note

If you disable QUIC by removing HTTP/3 in Services ‣ Caddy Web Server ‣ General Settings ‣ Advanced Settings, the Caddy Reverse Proxy HTTPS rule only needs TCP as protocol.

Standard Configuration

Note

The tutorial section implies that Prepare OPNsense for Caddy after installation has been followed.

Creating a Simple Reverse Proxy

Attention

The domain has to be externally resolvable. Create an A-Record with an external DNS Provider that points your domain to the external IP address of your OPNsense.

Go to Services ‣ Caddy Web Server ‣ General Settings

  • Check Enabled to enable Caddy
  • Input a valid email address into the Acme Email field. This is mandatory to receive automatic Let’s Encrypt and ZeroSSL certificates
  • Auto HTTPS should be set to On (default)
  • Press Apply

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Press Step 1: Add Domain. This will be the frontend that receives the traffic for the chosen domain name.

Options

Values

Frontend

Protocol:

https://

Domain:

foo.example.com

Port:

Leave empty

Certificate:

ACME (HTTP-01, TLS-ALPN-01)
  • Press Save
  • Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Handlers
  • Press Step 2: Add HTTP Handler. This will create a HTTP Handler that routes the traffic from the frontend domain to the an internal service.

Options

Values

Frontend

Domain:

https://foo.example.com

Upstream

Protocol:

http:// or https:// - depending on your upstream webserver

Upstream Domain:

192.168.10.1

Upstream Port:

80 - or set the port required by your upstream webserver

TLS Insecure Skip Verify

X - if https:// was chosen
  • Press Save and Apply

The automatic certificate will be installed, check the Logfile if there are errors. Now the frontend domain foo.example.com:80/443 receives all requests, and reverse proxies them to the upstream destination 192.168.10.1:80 (or custom port).

And that’s it, a working reliable reverse proxy in less than a minute. There are a lot of additional options, but this is essentially all that is needed for simple setups.

Tip

There is a Caddy Certificate Dashboard widget that shows all issued automatic certificates.

Note

TLS Insecure Skip Verify can be used in private networks. If the upstream destination is in an insecure network, like the internet or a dmz, consider using proper certificate handling.

Restrict Access to Internal IPs

Since the reverse proxy will accept all connections, restricting access with a firewall rule would impact all domains. Access Lists can restrict access per domain. In this example, they are used to restrict access to only internal IPv4 networks, refusing connections from the internet.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Access ‣ Access Lists

  • Press + to create a new Access List

Options

Values

Access List Name:

private_ipv4

Client IP Addresses:

192.168.0.0/16 172.16.0.0/12 10.0.0.0/8

Description:

Allow access from private IPv4 ranges

  • Press Save

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Edit an existing Domain or Subdomain and expand the Access Tab.

Options

Values

Access List:

private_ipv4

  • Press Save and Apply

Now, all connections without a private IPv4 address will be blocked. Some applications might demand a HTTP Error code instead of having their connection blocked, an example are monitoring systems. For these a custom HTTP Response Code can be set in the advanced mode.

Note

Access Lists can be set on Domains, Subdomains and HTTP Handlers. Setting them on Domains or Subdomains is recommended for simplicity.

Restrict Access with Basic Auth

Since the reverse proxy will accept all connections, restricting access with a firewall rule would impact all domains. Basic Auth will restrict access to one or multiple users.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Access ‣ Basic Auth

  • Press + to create a new User

Options

Values

User:

John

Password:

RandomPassword

  • Press Save and create additional Users if needed, e.g. Sarah.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Edit an existing Domain or Subdomain and expand the Access Tab.

Options

Values

Basic Auth:

John, Sarah

  • Press Save and Apply

Now, all anonymous connections have to authenticate with Basic Auth before accessing the reverse proxied service.

Note

Using CrowdSec is recommended. It will log authentication errors, and will ban these IP addresses. This prevents password bruteforcing.

Dynamic DNS

Supported Dynamic DNS Providers and requests for additions can be found here.

Tip

Read the full help text for guidance. It could also be necessary to check the selected provider module at Caddy DNS for further instructions. These modules are community maintained. When a module introduces issues that are not fixed it will be removed from this plugin.

Note

Enabling the Dynamic DNS checkboxes can have different results based on domain type. Enable it only where you need it, and test how your provider requires it for your hosted DNS zone:

  • Base Domain: example.com @

  • Wildcard Domain: example.com *

  • Subdomain: example.com opn

Use subdomains if you see errors in the log like:

failed setting DNS record(s) with new IP address(es)”,”zone”:”opn.example.com”,”error”:”expected 1 zone, got 0

This means the zone opn.example.com @ does not exist, and the provider expects example.com opn for the update. You can see the current configuration in Services ‣ Caddy Web Server ‣ Diagnostics ‣ Caddyfile.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ DNS Provider

  • Select one of the supported DNS Providers from the list

  • Input the DNS API Key, and any number of the additional required fields in Additional Fields.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ Dynamic DNS

  • Choose if DynDns IP Version should include IPv4 and/or IPv6.

  • Press Save

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Press + to create a new Domain. mydomain.duckdns.org is an example if duckdns is used as DNS Provider.

Options

Values

Domain:

mydomain.duckdns.org

Dynamic DNS:

X

Go to Services - Caddy Web Server - Reverse Proxy – HTTP Handlers

  • Press + to create a new HTTP Handler

Options

Values

Domain:

mydomain.duckdns.org

Upstream Domain:

192.168.1.1

  • Press Save and Apply

Check the Logfile for the DynDNS updates. Set it to Informational and search for the chosen domain.

Wildcard Domain with Subdomains

Note

If you use Dynamic DNS, subdomains are needed due to the way the API updates the DNS Records in hosted zones. For DNS Providers like Cloudflare, this is the recommended setup.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ DNS Provider

  • Select one of the supported DNS Providers from the list

  • Input the DNS API Key, and any number of the additional required fields in Additional Fields. Read the full help for details.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Create *.example.com as domain and activate the DNS-01 Challenge checkbox. Alternatively, use a certificate imported or generated in System ‣ Trust ‣ Certificates. It has to be a wildcard certificate.
  • Create all subdomains in relation to the *.example.com domain, for example foo.example.com and bar.example.com.
  • Check Dynamic DNS for the new subdomains, if needed.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Handlers

  • Create a HTTP Handler with *.example.com as domain and foo.example.com as subdomain. Most of the same configuration as with base domains are possible. The subdomain dropdown only shows when a wildcard domain has been configured.

Note

The certificate of a wildcard domain will only contain *.example.com, not a SAN for example.com. If there is a service that should match example.com exactly, create an additional domain for example.com with an additional HTTP Handler for its upstream destination. Subdomains do not support setting ports, they will always track the ports of their assigned parent wildcard domain.

Tip

If a domain should listen on more than one port, add it multiple times. The domains will automatically share the same wildcard certificate.

  • *.example.com:443

  • *.example.com:8443

Afterwards inherit the port from the domain by choosing it in the Subdomains tab. The same subdomain can be created multiple times under different wildcard domains if it should be available on multiple ports. To tell multiple same subdomains apart, give them a description with their port. Each of these subdomains need their own HTTP Handlers.

Reverse Proxy the OPNsense WebGUI

Tip

The same approach can be used for any upstream destination using TLS and a self-signed certificate.

Attention

The OPNsense WebGUI is only bound to 127.0.0.1 when no specific interface is selected: System ‣ Settings ‣ Administration - Listen Interfaces - All (recommended). Otherwise, use the IP address of the specific interface as “Upstream Domain”.
When setting Enable syncookies to always in Firewall ‣ Settings ‣ Advanced, reverse proxying the WebGUI is currently not possible. Set it to an adaptive setting, or never (default).
  • Open the OPNsense WebGUI in a browser (e.g. Chrome or Firefox). Inspect the certificate by clicking on the 🔒 in the address bar. Copy the SAN for later use. It can be a hostname, for example OPNsense.localdomain
  • Save the certificate as .pem file. Open it up with a text editor, and copy the contents into a new entry in System ‣ Trust ‣ Authorities. Name the certificate opnsense-selfsigned
  • Add a new Domain, for example opn.example.com
  • Add a new HTTP Handler with the following options:

Options

Values

Frontend

Domain:

opn.example.com

Upstream

Protocol

https://

Upstream Domain:

127.0.0.1

Upstream Port:

8443 - WebGUI Port

TLS Trust Pool:

opnsense-selfsigned

TLS Server Name:

OPNsense.localdomain

  • Press Save and Apply

Go to System ‣ Settings ‣ Administration

  • Input opn.example.com in Alternate Hostnames to prevent the error: The HTTP_REFERER “https://opn.example.com/” does not match the predefined settings

  • Press Save

Open https://opn.example.com and it should serve the reverse proxied OPNsense WebGUI. Check the log file for errors if it does not work, most of the time the TLS Server Name doesn’t match the SAN of the TLS Trust Pool. Caddy does not support certificates with only a CN Common Name.

Attention

Create an Access List to restrict access to the WebGUI.

Redirect ACME HTTP-01 Challenge

Sometimes an application behind Caddy uses its own ACME Client to get certificates, most likely with the HTTP-01 challenge. This plugin has a built in mechanism to redirect this challenge type easily to a destination behind it.

Make sure the chosen domain is externally resolvable. Create an A-Record with an external DNS Provider that points to the external IP Address of the OPNsense. In case of IPv6 availability, it is mandatory to create an AAAA-Record too, otherwise the TLS-ALPN-01 challenge might fail.

The configured Domain must use an empty port or 443 in the GUI, otherwise it can not use the TLS-ALPN-01 challenge for itself. The upstream destination must listen on Port 80 and serve /.well-known/acme-challenge/, for the same Domain that is configured in Caddy.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Press ✎ and open an existing Domain or Subdomain and enable advanced mode

Options

Values

Domain:

foo.example.com

HTTP-01 Challenge Redirection:

192.168.10.1

  • Press Save and Apply

The HTTP-01 Challenge Redirection is active and the upstream destination located at 192.168.10.1 will be able to issue the certificate for the domain foo.example.com.

With this configuration, Caddy will choose the TLS-ALPN-01 challenge to get its own certificate for foo.example.com, and reverse proxy the HTTP-01 challenge to 192.168.10.1, where the upstream destination can listen on port 80 for foo.example.com. With TLS enabled in the Handler, an encrypted connection is automatically possible. The automatic HTTP to HTTPS redirection is also taken care of.

Filter by Domain

A large configuration can be challenging to navigate. To help, a filter functionality has been added to the top right corner of the Domains, Subdomains and HTTP Handlers tab, called Filter by Domain.

In Filter by Domain, one or multiple Domains can be selected, and as filter result, only their corresponding configuration will be displayed in Domains, Subdomains and HTTP Handlers. With the “Clear All” button the filter can be reset easily.

Advanced Configuration

Multiple HTTP Handlers for the same Domain

HTTP Handlers are not limited to one per domain or subdomain. If there are multiple different paths to handle (e.g. /foo/* and /bar/*), create a HTTP Handler for each of them.

When creating a HTTP Handler with an empty path, the templating logic will automatically place it last in the Caddyfile site block. This means, specific paths will always match before an empty path, regardless of their position in the configuration. This could be used to block specific paths with an Access List, route some paths to different upstreams, and then set an empty handle for all unmatched paths.

Different handling logics can be selected. E.g., handle_path to strip the path from all requests, or handle to preserve the path from all requests.

When using a mix of wildcard domains and subdomains, a HTTP Handler set exclusively on the wildcard domain will match after all subdomains. That way, all unmatched subdomains can be sent to a custom upstream.

Multiple domains with the same hostname and different ports can be created at the same time. E.g., opn.example.com:443 and opn.example.com:8443. Now the frontend can listen on multiple ports for the same domain. These domains will share the same certificate automatically if ACME manages them. Each of these sockets need their own HTTP Handler to proxy traffic.

An example Caddyfile could look like this:

# Reverse Proxy Domain: "531e7877-0b58-4f93-a9f0-54beee58bdea"
opn.example.com:443 {
        handle /private/* {
                @d72c1182-6f05-4c25-8d9f-6a226a9039ea {
                        not client_ip 192.168.0.0/16 172.16.0.0/12 10.0.0.0/8
                }
                handle @d72c1182-6f05-4c25-8d9f-6a226a9039ea {
                        abort
                }

                reverse_proxy 172.16.99.10:8443 {
                }
        }

        handle /different_upstream/* {
                reverse_proxy 192.168.1.33 {
                }
        }

        handle {
                reverse_proxy 172.16.99.10:8443 {
                }
        }
}
# Reverse Proxy Domain: "58760ae1-2409-4a6b-a6c4-d58b15706b55"
opn.example.com:8443 {
        handle_path /strip_this {
                reverse_proxy 10.10.10.10:8443 {
                }
        }
}

Tip

Access Lists can match directly on HTTP Handlers for more complex access control scenarios.

Reverse Proxy a Webserver with Vhosts

Sometimes it is necessary to alter the host header in order to reverse proxy to another webserver with vhosts.

Since Caddy passes the original host header by default (e.g. app.external.example.com), if the upstream destination listens on a different hostname (e.g. app.internal.example.com), it would not be able to serve this request.

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Press + to create a new Domain

Options

Values

Domain:

app.external.example.com

  • Press Save

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Headers

  • Press + to create a new HTTP Header

Options

Values

Header:

header_up

Header Type:

Host

Header Value:

{upstream_hostport}

  • Press Save

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ HTTP Handler

  • Press + to create a new HTTP Handler and enable advanced mode

Options

Values

Domain:

app.external.example.com

Upstream Domain:

app.internal.example.com

HTTP Headers:

header_up Host {upstream_hostport}

  • Press Save and Apply

CrowdSec Integration

CrowdSec is a powerful alternative to a WAF. It uses logs to dynamically ban IP addresses of known bad actors. The Caddy plugin is prepared to emit the json logs for this integration.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ Log Settings

  • Enable Log HTTP Access in JSON Format

  • Press Save

Go to Services ‣ Caddy Web Server ‣ Reverse Proxy ‣ Domains

  • Open each Domain that should be monitored by CrowdSec and open Access

  • Enable HTTP Access Log

Now the HTTP access logs will appear in /var/log/caddy/access in json format, one file for each domain.

Next, connect to the OPNsense via SSH or console, go into the shell with Option 8.

Attention

This step requires the os-crowdsec plugin.

  • Once in the shell, install the caddy collection from CrowdSec Hub. cscli collections install crowdsecurity/caddy

  • Create the configuration file as /usr/local/etc/crowdsec/acquis.d/caddy.yaml with the following content:

filenames:
  - /var/log/caddy/access/*.log

force_inotify: true
poll_without_inotify: true

labels:
  type: caddy

  • Go into the OPNsense WebGUI and restart CrowdSec.

High Availability Setups

There are a few possible configurations to run Caddy successfully in a High Availability Setup with two OPNsense firewalls.

The main issue is the certificate handling. If a CARP VIP is used on the WAN interface, and the A and AAAA Records of all domains point to this CARP VIP, the backup Caddy will not be able to issue ACME certificates without some additional configuration.

There are three methods that support XMLRPC sync:

Note

These methods can be mixed, just make sure to use a coherent configuration. It is best to decide for one method. Only Domains need configuration, Subdomains do not need any configuration for HA.

  1. Using custom certificates from the OPNsense Trust store for all Domains.

  2. Using the DNS-01 Challenge in the settings of Domains.

  3. Using the HTTP-01 Challenge Redirection option in the advanced settings of Domains.

Since the HTTP-01 Challenge Redirection needs some additional steps to work, it should be set up as followed:

  • Configure Caddy on the master OPNsense until the whole initial configuration is completed.
  • On the master OPNsense, select each Domain, and set the IP Address in HTTP-01 Challenge Redirection to the same value as in Synchronize Config to IP found in System ‣ High Availability ‣ Settings.
  • Create a new Firewall rule on the master OPNsense that allows Port 80 and 443 to This Firewall on the interface that has the prior selected IP Address (most likely a LAN or VLAN interface).
  • Sync this configuration with XMLRPC sync.

Now both Caddy instances will be able to issue ACME certificates at the same time. Caddy on the master OPNsense uses the TLS-ALPN-01 challenge for itself and reverse proxies the HTTP-01 challenge to the Caddy of the backup OPNsense. Please make sure, that the master and backup OPNsense are both listening on their WAN and LAN (or VLAN) interfaces on port 80 and 443, since both ports are required for these challenges to work.

Tip

Check the Logfile on both Caddy instances for successful challenges. Look for certificate obtained successfully informational messages.

Forward Auth

Delegating authentication to Authelia, before serving an app via reverse proxy, is a very advanced usecase. The Forward Auth Documentation should be used for inspiration.

To attach the Forward Auth directive to a handler, the Auth Provider has to be filled out in the General Settings. Afterwards, the Forward Auth checkbox in a Handler can be selected in advanced mode. This will prepend the forward_auth directive in front of the reverse_proxy directive in the scope of that Handler. Headers are set automatically.

Using Access Lists and Basic Auth in the Domain this Handler matches on is not recommended.

An example Caddyfile could look like this:

app1.example.com {
    handle {
        forward_auth authelia:9091 {
            uri /api/verify?rd=https://auth.example.com
            copy_headers Remote-User Remote-Groups Remote-Name Remote-Email
        }
        reverse_proxy 192.168.10.1:8080 {
        }
    }
}

Requests from clients to app1.example.com will be sent to Authelia via the forward_auth directive. Then, after the authentication has been completed, the reverse_proxy directive sends the traffic to the Upstream.

Run Caddy Process Unprivileged

In this plugin, Caddy runs as root. This is required when well-known ports are used. Since the default ports are 80 and 443, Caddy will be started as superuser.

For higher security demands, there is the option to run Caddy as www user and group. This comes with the restriction of only being able to use upper ports (≥ 1024).

Make sure all of the domains have empty ports, or ports above the well-known port range before continuing. There is a validation that will prevent configuring well-known ports when the www user is active.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ Advanced Settings

  • Add custom upper HTTP Port, e.g. 8080
  • Add custom upper HTTPS Port, e.g. 8443
  • Select www as System User
  • Restart Caddy completely. Disable it and press Apply, then enable it and press Apply.

From now on, Caddy will run as www user and group. This can be verified by checking the user of the Caddy process.

Note

With this configuration, Port Forward should be used to forward port 80 and 443 to the new alternative HTTP and HTTPS Ports. For IPv6 additional steps could be required.

Bind Caddy to Interfaces

Warning

Binding a service to a specific interface via IP address can cause lots of issues. If the IP address is dynamic, the service can crash or refuse to start. During boot, the service can refuse to start if the interface IP addresses are assigned too late. Configuration changes on the interfaces can cause the service to crash. Only use this with static IP addresses! There is no OPNsense community support for this configuration.

This configuration is only useful if there are two or more WAN interfaces, and Caddy should only respond on one of them. It can also solve port conflicts, for example if one interface should DNAT or host a different service with the default webserver ports.

  • Create the following files with the following content in the OPNsense filesystem:

  1. /usr/local/etc/caddy/caddy.d/defaultbind.global

default_bind 203.0.113.1 192.168.1.1

  1. /usr/local/etc/caddy/caddy.d/defaultbind.conf

http:// {
bind 203.0.113.1 192.168.1.1
}

Now Caddy will only bind to 203.0.113.1 and 192.168.1.1. It can still be configured in the GUI without restrictions.

Read more about the default_bind directive: Default Bind

Custom Configuration Files

  • The Caddyfile has an additional import from the path /usr/local/etc/caddy/caddy.d/. Place custom configuration files inside that adhere to the Caddyfile syntax.
  • *.global files will be imported into the global block.
  • *.conf files will be imported into the site block.
  • *.layer4global and *.layer4listener files will be imported into their respective layer4 directive.
  • Don’t forget to test the custom configuration with caddy validate --config /usr/local/etc/caddy/Caddyfile.

With these imports, the full potential of Caddy can be unlocked. The GUI options will remain focused on the reverse proxy. There is no OPNsense community support for configurations that have not been created with the offered GUI. For customized configurations, the Caddy community is the right place to ask.

Caddy: Layer4 Proxy

Enable Layer4 Proxy

  • Go to Services ‣ Caddy Web Server ‣ General Settings
  • Enable the checkbox Enable Layer4 Proxy
  • Press Apply, then go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

Routing Type

The implementation has two different modes for layer4 routes:

  1. listener_wrappers will match traffic on the default HTTP and HTTPS ports that Caddy listens on. With a Layer 7 matcher, selected protocols can be proxied to an upstream. This can be used to multiplex protocols on the default ports and still use the Reverse Proxy at the same time. The most popular usecase is proxying HTTPS without TLS termination. As default route, all unmatched traffic will be sent to the Reverse Proxy.

  2. global can match any TCP/UDP traffic on any free local port. Additionally, one or multiple Layer 7 matchers can be created under the same protocol port combination. The sequence can be set manually by changing the sequence number.

Routes for both modes can be used at the same time.

Layer 4 Matchers

For the global routing type, the protocol can be set to either TCP or UDP. A local port must be selected, this port must be free and not used by any other service. Port ranges are not supported.

Any IP traffic that matches the port and protocol can proxied to one or multiple upstreams. If raw Layer 4 traffic should be proxied, select ANY as Layer 7 matcher.

Layer 7 Matchers

A Layer 7 matcher checks the first bytes of a TCP/UDP packet and decides which protocol it could be. When TLS or HTTP is detected, they can inspect the contents of the Client Hello at the start of a TLS handshake, or the Host Header in case of HTTP traffic.

There are additional matchers for all kinds of protocols, including:

  • DNS

  • HTTP (with and without Host Header evaluation)

  • Postgres

  • Proxy Protocol

  • RDP

  • SOCKSv4/v5

  • SSH

  • TLS (with and without Client Hello evaluation)

  • Wireguard

  • XMPP

Configuration Examples

SSH Multiplexing on HTTPS Port

SSH is a raw protocol matcher, it will match all traffic that looks like SSH in the scope of either the listener_wrapper, or a TCP port in global. Host Headers or SNI can not be evaluated since SSH does not send this information.

In this example, we want to allow SSH on the default HTTPS port. This will route the SSH traffic to a selected upstream and all unmatched traffic to the Reverse Proxy.

  • Go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

  • Press + to create a new Layer4 Route

Options

Values

Matchers:

SSH

Upstream Domain:

192.168.1.1

Upstream Port:

22

  • Press Save and Apply

Now an SSH client can open a connection like ssh app1.example.com -p 443 and the SSH traffic will go through the same port as other HTTP/HTTPS traffic. Caddy becomes a protocol multiplexer.

Tip

If another route is added, e.g. with the RDP matcher, then SSH and RDP will be on the same port but can be proxied to different upstreams.

TLS (SNI) Multiplexing on HTTPS Port

There is an application with the hostname app1.example.com which should not be handled by the HTTP Handlers of the Reverse Proxy. The TLS traffic of this application should be routed directly to an upstream destination without TLS termination.

  • Go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

  • Press + to create a new Layer4 Route

Options

Values

Domain:

app1.example.com

Matchers:

TLS (SNI)

Upstream Domain:

192.168.1.1

Upstream Port:

8443

  • Press Save and Apply

Caddy listens on the default HTTP and HTTPS ports. All traffic it receives on these or any other listening ports, gets passed to the listener_wrapper. Inside this wrapper, the traffic can be inspected on Layer 7, and routing decisions can be made.

With the matcher TLS (SNI), the Client Hello of the TLS traffic is analyzed. When the Client Hello includes app1.example.com, the traffic will be matched by the new Layer4 Route. The raw TLS traffic will be streamed to the chosen upstream socket.

Any other traffic that is not matched by this Layer4 Route will be routed to the HTTP Handlers, where the configured Domains and Subdomains can receive and reverse proxy it.

Note

When Auto HTTPS is enabled, all clients will be permanently redirected to HTTPS automatically. If that should not happen, set it to Disable Redirects.

Inverted TLS (SNI) Multiplexing on HTTPS Port

Inverting the TLS (SNI) matcher can route all unmatched traffic, for example to a hosting panel where the domains are not under administrative control and can change at any time. The domains matched by SNI will be routed to the Reverse Proxy.

Attention

If you create additional routes, e.g., for SSH, make sure to use the sequence number to generate them before this route.

  • Go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

  • Press + to create a new Layer4 Route

  • Enable the advanced mode toggle

Options

Values

Sequence:

100

Routing Type:

listener_wrappers

Protocol:

TCP

Matchers:

TLS (SNI)

Domain:

*.example.com *.opnsense.com

Invert Matchers:

X

Upstream Domain:

192.168.1.1 192.168.1.2

Upstream Port:

443

Fail Duration:

10

  • Press Save and Apply

With the inverted TLS (SNI) matcher, the Client Hello of the TLS traffic is analyzed. When the Client Hello includes either of *.example.com or *.opnsense.com, the traffic will be sent to the default HTTP Handlers, where the configured Domains and Subdomains can receive and reverse proxy it.

All other traffic will be streamed to the chosen socket of Upstream Domain and Upstream Port. Since we chose multiple upstreams and a health check, two servers can load balance all requests. The load balancing is just an example, and not necessary for this matcher to work.

Tip

If there are domains inside *.example.com that should be routed to a different upstream, just create an additional TLS (SNI) matcher for them. Set the sequence to a lower number to match it before the inverted route.

Tip

Caddy supports the HA Proxy Protocol. If the Protocol Header should be added to the upstream, set the Proxy Protocol version to v1 or v2.

Proxy TCP/UDP on Layer 4

We have an application that should receive all TCP/UDP traffic directed at port 5060.

  • Go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

  • Press + to create a new Layer4 Route

  • Enable the advanced mode toggle

Options

Values

Routing Type:

global

Protocol:

TCP

Local Port:

5060

Matchers:

ANY

Upstream Domain:

192.168.1.1

Upstream Port:

5060

  • Press Save and + to create another Layer4 Route

Options

Values

Routing Type:

global

Protocol:

UDP

Local Port:

5060

Matchers:

ANY

Upstream Domain:

192.168.1.1

Upstream Port:

5060

  • Press Save and Apply

DNS and Wireguard Multiplexing

We have a DNS server that hosts one of our DNS zones. We want to allow Wireguard on the same port as DNS, but only from a certain remote ip range.

Note

The sequence is optional, but it can influence the processing order of created rules.

  • Go to Services ‣ Caddy Web Server ‣ Layer4 Proxy

  • Press + to create a new Layer4 Route

  • Enable the advanced mode toggle

Options

Values

Sequence:

100

Routing Type:

global

Protocol:

UDP

Local Port:

53

Matchers:

DNS

Upstream Domain:

192.168.1.1

Upstream Port:

53

  • Press Save and + to create another Layer4 Route

Options

Values

Sequence:

101

Routing Type:

global

Protocol:

UDP

Local Port:

53

Matchers:

Wireguard

Upstream Domain:

172.16.1.1

Upstream Port:

51820

Remote IP:

203.0.113.0/24

  • Press Save and Apply

All of these Layer 7 routes will be automatically grouped under port UDP/53 in the chosen sequence order.

Caddy: Troubleshooting

FAQ

  • A DNS Provider is not required to get automatic certificates.
  • Port Forwards, NAT Reflection, Split Horizon DNS or DNS Overrides in Unbound are not required. Only create Firewall rules that allow traffic to the default ports of Caddy.
  • Even though internal clients will use the external IP address to access the reverse proxied services, the traffic will not pass over the internet. It will stay inside the OPNsense. Only in rare cases where there is multi WAN, the traffic can be routed from one WAN interface to the other over the internet, due to reply-to settings.
  • Firewall rules to allow Caddy to reach internal services are not required. OPNsense has a default rule that allows all traffic originating from itself to be allowed.
  • ACME clients on reverse proxied upstream destinations will not be able to issue certificates. Caddy intercepts /.well-known/acme-challenge. This can be solved by using the HTTP-01 Challenge Redirection option in the advanced mode of domains. Please check the tutorial section for an example.
  • When using Caddy with IPv6, the best choice is to have a GUA (Global Unicast Address) on the WAN interface, since otherwise the TLS-ALPN-01 challenge might fail.
  • Let’s Encrypt or ZeroSSL can not be explicitely chosen. Caddy automatically issues one of these options, determined by speed and availability. These certificates can be found in /var/db/caddy/data/caddy/certificates.
  • When an Upstream Destination only supports TLS connections, yet does not offer a valid certificate, enable TLS Insecure Skip Verify in a Handler to mitigate connection problems.
  • Caddy upgrades all connections automatically from HTTP to HTTPS. When cookies do not have have the secure flag set by the application serving them, they can still be transmitted unencrypted before the connection is upgraded. If these cookies contain very sensitive information, it might be a good choice to close port 80.
  • There is optional Layer4 TCP/UDP routing support. In the scope of this plugin, only traffic that looks like TLS and has SNI can be routed. The HTTP App and Layer4 App can work together at the same time.
  • There is no WAF (Web Application Firewall) support in this plugin. For a business grade Reverse Proxy with WAF functionality, use os-OPNWAF. As an alternative to a WAF, it is simple to integrate Caddy with CrowdSec. Check the tutorial section for guidance.

Help, Nothing Works!

Note

Even though Caddy itself is quite easy to configure in the plugin, setting the infrastructure up correctly poses the real challenge. If you feel stumped, the best approach is knowledge about what should happen. This section tries to explain that and gives examples how to resolve issues.

Tip

Most errors happen because the infrastructure is not set up correctly, or wrong options for the HTTP Handler have been set.

Attention

Do not use the Layer4 module without knowing the implications of it. It is for very advanced usecases. Better deactivate it if things do not work as expected.

This is what should happen if Caddy works correctly:

  1. A Web Browser is opened and an URL is put into the address bar: https://example.com
  2. The underlying Operating System of the Web Browser sends a request to its default DNS Server, and asks where to find example.com. The DNS Server will try to find the requested A- and/or AAAA-Record for that domain, and will answer with e.g. 203.0.113.1.
  3. The Web Browser now sends a HTTPS request to 203.0.113.1. This request contains a Client Hello in the TLS handshake, that contains example.com.
  4. This HTTPS request hits port 443 of the OPNsense’s WAN, LAN (or VPN) interface, determined by the network location of the Web Browser.
  5. There is a Firewall rule that allows destination port 443 to access This Firewall. The request will then be received by Caddy, because it listens on This Firewall on port 443.
  6. In Caddy, there is a domain for example.com set up. It has a valid Let’s Encrypt or ZeroSSL certificate. Since the Client Hello contains example.com, Caddy will match it with the domain, and the Web Browser shows a certificate next to https://example.com in the address bar.
  7. Caddy takes the HTTPS request and terminates the TLS connection. That means, it will convert the HTTPS into HTTP, so it can be processed by the HTTP Handler.
  8. Caddy checks if there is a matching HTTP Handler set up. It will be used to reverse proxy the HTTP request to an internal service.
  9. Inside the HTTP Handler, the domain example.com and an Upstream Domain e.g. 192.168.10.1 and Upstream Port e.g. 8080 point the request to the internal service. Caddy then sends the HTTP request directly to the internal service.
  10. The HTTP response from the internal service is received by Caddy, wrapped back into TLS, and sent back to the Web Browser as HTTPS response.
  11. The website of the internal service shows up in the Web Browser, secured by HTTPS.

Attention

If that does not work, it means that one or multiple steps in that chain of events fail. Please check the following steps for initial troubleshooting.

1. Check the Infrastructure:

  • Do A- and/or AAAA-Record for all Domains and Subdomains exist?

  • In case of activated Dynamic DNS, check that the correct A- and/or AAAA-Records have been set automatically with the DNS Provider.

  • Do they point to one of the external IPv4 or IPv6 addresses of the OPNsense Firewall? Check that with commands like nslookup example.com

  • Do the OPNsense Firewall Rules allow connections from any source to destination ports 80 and 443 to the destination This Firewall?

  • Is the Caddy service running?

2. Check if the Domain is set up correctly:

  • Open the Domain in a Web Browser. Inspect the certificate by clicking on the 🔒 in the address bar. It should be a Let’s Encrypt, ZeroSSL or custom certificate (if chosen).

  • Activate the HTTP Access Log in a Domain, and check the Log File. Are there any log entries that show connections?

  • If nothing shows up, go back to Step 1 and check the infrastructure.

3. Check the functionality of the internal webserver:

  • Does the service accept HTTP or HTTPS connections? It is recommended to connect via HTTP, since it removes complexity.

  • Open the internal service via IP address and port in a Web Browser, e.g. http://192.168.10.1:8080. Validate that it shows the website on either HTTP or HTTPS ports.

  • Does the internal service actually use the HTTP or HTTPS protocol? Other protocols will not work, e.g. SSH.

  • If the Web Browser can not connect, it is a good idea to troubleshoot the internal webserver before continuing.

4. Check the setup of the HTTP Handler:

  • Is the correct Domain chosen?

  • Are Upstream Domain and Upstream Port correct? Do they point to the internal service, e.g 192.168.10.1:8080?

  • If the internal service only accepts HTTPS connections, is https:// chosen and TLS insecure skip verify checked?

Attention

If the configuration is still not working, it is time to continue with logs and Caddyfile syntax checks.

Get Help from the Caddy Community

Sometimes, things do not work as expected. Caddy provides a few powerful debugging tools to analyze issues.

This section explains how to obtain the required files to get help from the Caddy Community.

  1. Change the global Log Level to DEBUG. This will log everything the reverse_proxy directive handles.

Go to Services ‣ Caddy Web Server ‣ General Settings ‣ Log Settings

  • Set the Log Level to DEBUG

  • Press Apply

Go to Services ‣ Caddy Web Server ‣ Log File

  • Change the dropdown from INFORMATIONAL to DEBUG

Now the reverse_proxy debug logs will be visible and can be downloaded.

  1. Validate and download the Caddyfile.

Go to Services ‣ Caddy Web Server ‣ Diagnostics ‣ Caddyfile

  • Press the Validate Caddyfile button to make sure the current Caddyfile is valid. Refresh the page afterwards to ensure the Caddyfile is correctly formatted.
  • Press the Download button to get this current Caddyfile.
  • If there are custom imports in /usr/local/etc/caddy/caddy.d/, download the JSON configuration.

Attention

Rarely, a performance profile might be requested. For this, a special admin endpoint can be activated. This admin endpoint is deactivated by default. To enable it and access it on the OPNsense, follow these additional steps. Do not forget to deactivate it after use. Anybody with network access to the admin endpoint can use REST API to change the running configuration of Caddy, without authentication.

  • SSH into the OPNsense shell
  • Stop Caddy with configctl caddy stop
  • Go to /usr/local/etc/caddy/caddy.d/
  • Create a new file called admin.global and put the following content into it: admin :2019
  • After saving the file, go to /usr/local/etc/caddy and run caddy validate to ensure the configuration is valid.
  • Start Caddy with configctl caddy start
  • Use sockstat to see if the admin endpoint has been created. sockstat -l | grep -i caddy - it should show the endpoint *:2019.
  • Create a firewall rule on LAN that allows TCP to destination This Firewall and destination port 2019.
  • Open the admin endpoint: http://YOUR_LAN_IP:2019/debug/pprof/
  • Follow the instructions on Profiling Caddy.