CADDY-DOCKER-PROXY

Introduction

This plugin enables caddy to be used as a reverse proxy for Docker.

How does it work?

It scans Docker metadata looking for labels indicating that the service or container should be exposed on caddy.

Then it generates an in memory Caddyfile with website entries and proxies directives pointing to each Docker service DNS name or container IP.

Every time a docker object changes, it updates the Caddyfile and triggers a caddy zero-downtime reload.

Basic labels

To expose a service or container inside caddy configuration, you just need to add labels starting with caddy.

Those are the main labels that configures the basic behavior of the proxying:

Label	Example	Description	Required
caddy.address	service.example.com	addresses that should be proxied separated by whitespace	Required
caddy.targetport	80	the port being server by container	Optional
caddy.targetpath	/api	the path being served by container	Optional
caddy.targetprotocol	https	the protocol being served by container	Optional

When added to a service, the values above will generate the following caddy configuration:

service.example.com {
	proxy / servicedns:80/api
}

Proxying services vs containers

Caddy docker proxy is able to proxy to swarm servcies or raw containers. Both features are always enabled, and what will differentiate the proxy target is where you define your labels.

Services

To proxy swarm services, labels should be defined at service level. On a docker-compose file, that means labels should be inside deploy, like:

service:
  ...
  deploy:
    caddy.address=service.example.com
    caddy.targetport=80

Caddy will use service dns name as target, swarm takes care of load balancing into all containers of that service.

Containers

To proxy containers, labels should be defined at container level. On a docker-compose file, that means labels should be outside deploy, like:

service:
  ...
  caddy.address=service.example.com
  caddy.targetport=80

When proxying a container, caddy uses a single container IP as target. Currently multiple containers/replicas are not supported under the same website.

Usage examples

Proxying domain root to container root

caddy.address=service.example.com
caddy.targetport=80

Proxying domain root to container path

caddy.address=service.example.com
caddy.targetport=80
caddy.targetpath=/my-path

Proxying domain path to container root

caddy.address=service.example.com/path1
caddy.targetport=80

Proxying domain path to container path

caddy.address=service.example.com/path1
caddy.targetport=80
caddy.targetpath=/path2

Proxying multiple domains to container

caddy.address=service1.example.com service2.example.com
caddy.targetport=80

More labels

Any other label prefixed with caddy, will also be converted to caddyfile configuration based on the following rules:

Label's keys are transformed into a directive and its value becomes the directive arguments. Example:

caddy.directive=valueA valueB

Generates:

directive valueA valueB

Dots represents nested directives. Example:

caddy.directive=argA
caddy.directive.subdirA=valueA
caddy.directive.subdirB=valueB1 valueB2

Generates:

directive argA {
	subdirA valueA
	subdirB valueB1 valueB2
}

Labels for parent directives are not required. Example:

caddy.directive.subdirA=valueA

Generates:

directive {
	subdirA valueA
}

Labels with empty values generates directives without arguments. Example:

caddy.directive=

Generates:

directive

It's possible to add directives to the automatically created proxy directive. Example:

caddy.proxy.websocket=

Generates:

service.example.com {
	proxy / servicedns:80/api {
		websocket
	}
}

Any _# suffix on labels is removed when generating caddyfile configuration, that allows you to write repeating directives. Example:

caddy.directive_1=value1
caddy.directive_2=value2

Generates:

directive value1
directive value2

Multiple caddyfile sections from one service/container

It's possible to generate multiple caddyfile sections for the same service/container by suffixing the caddy prefix with _#. That's usefull to expose multiple service ports at different urls.

For example:

caddy_0.address = portal.example.com
caddy_0.targetport = 80
caddy_1.address = admin.example.com
caddy_1.targetport = 81

Generates:

portal.example.com {
	proxy / servicedns:80
}
admin.example.com {
	proxy / servicedns:81
}

Docker images

Docker images are available at Docker Registry: https://hub.docker.com/r/lucaslorentz/caddy-docker-proxy/

Caddy CLI

All flags and environment variables supported by Caddy CLI are also supported: https://caddyserver.com/docs/cli

Check examples folder to see how to set them on a docker compose file.

This plugin provides these flags:

  -docker-label-prefix string
        Prefix for Docker labels (default "caddy")
  -proxy-service-tasks
        Proxy to service tasks instead of VIP

Those flags can also be set via environment variables:

CADDY_DOCKER_LABEL_PREFIX=<string>
CADDY_DOCKER_PROXY_SERVICE_TASKS=<bool>

Connecting to Docker Host

The default connection to docker host varies per platform:

• At Unix: unix:///var/run/docker.sock
• At Windows: npipe:////./pipe/docker_engine

You can modify docker connection using the following environment variables:

• DOCKER_HOST: to set the url to the docker server.
• DOCKER_API_VERSION: to set the version of the API to reach, leave empty for latest.
• DOCKER_CERT_PATH: to load the tls certificates from.
• DOCKER_TLS_VERIFY: to enable or disable TLS verification, off by default.

Volumes

On a production docker swarm cluster, it's very important to store Caddy folder on a persistent storage. Otherwise Caddy will re-issue certificates every time it is restarted, exceeding let's encrypt quota.

To do that map a docker volume to /root/.caddy folder.

Since Caddy version 0.10.11, it is possible to run multiple caddy instances sharing same certificates.

For resilient production deployments, use multiple caddy replicas and map a/root/.caddy folder to a volume that supports multiple mounts, like Network File Sharing docker volumes plugins.

Here is an example of compose file with replicas and persistent volume using Rexray EFS Plugin for AWS.

Trying it

Clone this repository.

Deploy the compose file to swarm cluster:

docker stack deploy -c examples/service-proxy.yaml caddy-docker-demo

Wait a bit for services startup...

Now you can access both services using different urls

curl -H Host:whoami0.example.com http://localhost:2015

curl -H Host:whoami1.example.com http://localhost:2015

curl -H Host:config.example.com http://localhost:2015

After testing, delete the demo stack:

docker stack rm caddy-docker-demo

Building it

You can use our caddy build wrapper build.sh and include additional plugins on https://github.com/lucaslorentz/caddy-docker-proxy/blob/master/main.go#L5

Or, you can build from caddy repository and import caddy-docker-proxy plugin on file https://github.com/mholt/caddy/blob/master/caddy/caddymain/run.go :

import (
  _ "github.com/lucaslorentz/caddy-docker-proxy/plugin"
)