A Docker ambassador (containerized TCP reverse proxy / forwarder) that supports static forwards, DNS-based forwards (with SRV), Consul+Etcd based forwards, or forwards based on the connecting container's intended backend (read: magic).
You can get the ambassadord container from the Docker Hub. It is a trusted build.
$ docker pull progrium/ambassadord
There are two ways to use ambassadord. The first is called standard mode, where it acts as an ambassador for one pre-defined type of backend. This is most like the normal ambassador pattern, but with support for dynamic backend lookups.
The second is called omni mode, where it can be used for any type of backend based on data provided by the connecting container's environment. Using omni mode means you only need to run one ambassador on a host, then all containers can use it for connecting to all their dependent backends.
Ambassador to fixed/resolved backend(s) using domain or IP and port. Listens on same port as destination.
$ docker run -d --expose 8080 progrium/ambassadord 192.168.1.100:8080
$ docker run -d --expose 6379 progrium/ambassadord redis.example.com:6379
$ docker run -d --expose 6379 progrium/ambassadord redis-1.example.com:6379,redis-2.example.com:6379
Ambassador to fixed backend defined by container link(s). Listens on the same ports as the link ports.
$ docker run -d --expose 6379 --link redis:redis progrium/ambassadord --links
$ docker run -d --expose 6379 --expose 8080 --link redis:redis --link http:http progrium/ambassadord --links
Ambassador to backends resolved using SRV from DNS (ie Consul service discovery). Always listens on default exposed port 10000.
$ docker run -d progrium/ambassadord redis.service.consul
Ambassador to backends found in configuration KV store. Uses the values of child nodes if the path has children, otherwise, uses the value found at the given path. Lookups are cached and updated when the value changes in the configuration store. Always listens on exposed port 10000.
$ docker run -d progrium/ambassadord etcd://127.0.0.1:4001/path/to/backend/nodes
$ docker run -d progrium/ambassadord consul://127.0.0.1:8500/path/to/backend/nodes
Start the ambassador in omni mode, passing the Docker socket:
$ docker run -d -v /var/run/docker.sock:/var/run/docker.sock --name backends progrium/ambassadord --omnimode
This container, named backends, listens on exported port 10000, but needs to handle connections on all ports on its interface. To configure this, we run another ambassadord container with --privileged attached to the backends container's network, and we tell it to set up iptables for the ambassadord container:
$ docker run --rm --privileged --net container:backends progrium/ambassadord --setup-iptables
Now we can start other containers that use ambassadord. They must be linked to the ambassadord container and specify their outgoing connection backends via BACKEND environment variables. For example, here we start a container that will have outgoing connections on 6379 sent to the backend defined by DNS SRV records for redis.services.consul:
$ docker run -d --link backends:backends -e "BACKEND_6379=redis.services.consul" progrium/mycontainer startdaemon
Inside this container, any connections to backends:6379 will be forwarded to backends resolved by redis.services.consul. You can set up multiple backends for several ports by adding more BACKEND environment variables using the port you'll be connecting with in the name and the backend to use in the value. Any of the backend definitions supported by standard mode can be used as a value.
This project was made possible thanks to DigitalOcean. Also thanks to Jérôme Petazzoni for helping me make the magic of omni mode work.
BSD