ETCD: A highly-available key value store for shared configuration and service discovery

This is a Radial Wheel repository for etcd. It is a copy of the official coreos/etcd image modified only to work within the Radial topology.

It is also configured to run etcdctl directly from the command line, using the same image as a wrapper:

docker run -it --rm -e "ETCDCTL_PEERS=http://192.168.1.1:4001" radial/etcd set foo bar

Note: Make sure the IP you pass to ETCDCTL_PEERS is routable from the inside of your container to wherever one of your etcd cluster nodes is.

Tunables

Tunable environment variables; modify at runtime. Italics are defaults. All environment variables names used here are the same as the default coreos/etcd container. These are mentioned here for sake of displaying default values specific to Radial.

• $SPOKE_CMD: ["etcdctl"] This variable sets the command to run, like an entrypoint, when passing arguments to docker run as demonstrated above. You could technically change it to anything, but you'll most likely just change it to etcd (if at all) if you like to use command line flags instead of environment variables or configuration for the etcd binary.
• $ETCD_DATA_DIR: ["/data/backup"] Location to store etcd backup snapshots and log files
• $ETCD_NAME: [container_id] Name for this etcd node.
• $RESET_DATA_ON_RESTART: ["False"] Whether to delete the snapshot and log data when the container is restarted. This is helpful during testing and when using the container as a discovery service.

Radial

Radial is a Docker container topology strategy that seeks to put the cannon of Docker best-practices into simple, re-usable, and scalable images, dockerfiles, and repositories. Radial categorizes containers into 3 types: Axles, Hubs, and Spokes. A Wheel is a repository used to recreate an application stack consisting of any combination of all three types of containers. Check out the Radial documentation for more.

One of the main design goals of Radial containers is simple and painless modularity. All Spoke (application/binary) containers are designed to be run by themselves as a service (a Wheel consisting of a Hub container for configuration and a Spoke container for the running binary) or as part of a larger stack as a Wheel of many Spokes all joined by the Hub container (database, application code, web server, backend services etc.). Check out the Wheel tutorial for some more details on how this works.

Note also that for now, Radial makes use of Fig for all orchestration, demonstration, and testing. Radial is just a collection of images and strategies, so technically, any orchestration tool can work. But Fig was the leanest and most logical to use for now.

How to Use

Static Build

In case you need to modify the entrypoint script, the Dockerfile itself, create your "config" branch for dynamic building, or just prefer to build your own from scratch, then you can do the following:

1. Clone this repository
2. Make whatever changes needed to configuration and add whatever files
3. fig up

Dynamic Build

A standard feature of all Radial images is their ability to be used dynamically. This means that since great care is made to separate the application code from it's configuration, as long as you make your application configuration available as a git repository, and in it's own "config" branch as per the guidelines in the Wheel template, no building of any images will be necessary at deploy time. This has many benefits as it allows rapid deployment and configuration without any wait time in the building process. However:

Dynamic builds will not commit your configuration files into any resulting images like static builds.

Static builds do a "COPY" of files into the image before exposing the directories as volumes. Dynamic builds do a git fetch at run time and the resulting data is downloaded to an already existing volume location, which is now free from Docker versioning. Both methods have their advantages and disadvantages. Deploying the same exact configuration might benefit from a single image built statically whereas deploying many different disposable configurations rapidly are best done dynamically with no building.

To run dynamically:

1. Modify the fig-dynamic.yml file to point at your own Wheel repository location by setting the $WHEEL_REPO variable. When run, the Hub container will pull the "config" branch of that repository and use it to run the Spoke container with your own configuration.
2. fig -f fig-dynamic.yml up