Implement docker healthchecks

[EdwinHoksberg]

Implement a healthcheck for all docker images. The healthcheck will execute a PING command to the redis server every 30 seconds. When this command fails by either a timeout of 5 seconds or unexpected output, the healthcheck will fail and trigger an event which a user can capture.

One thing I'm not sure about is the numbers I used, specifically for the interval(30s) and the timeout (5s). These can be changed if necessary.

Output in docker ps(see the status column):

# First 30 seconds when a container was started
CONTAINER ID        IMAGE                              COMMAND                  CREATED             STATUS                            PORTS                                              NAMES
455a1e6bf0c1        test/redis:latest                  "docker-entrypoint.s…"   2 minutes ago       Up 6 seconds (health: starting)   6379/tcp, 0.0.0.0:6379->63799/tcp                  test-redis

# After 30 seconds when the first healthcheck was executed
CONTAINER ID        IMAGE                              COMMAND                  CREATED             STATUS                    PORTS                                              NAMES
455a1e6bf0c1        test/redis:latest                  "docker-entrypoint.s…"   2 minutes ago       Up 42 seconds (healthy)   6379/tcp, 0.0.0.0:6379->63799/tcp                  test-redis

Full reference here: https://docs.docker.com/engine/reference/builder/#healthcheck
Fixes #91

[wglambert]

See docker-library/cassandra#76 (comment)

I do not feel that generalized healthchecks on the official images are really that useful . . .

The healthcheck repo serves as an example for creating your own image derived from the healthcheck-prototypes provided.

There is an example set of prototype images (available under https://hub.docker.com/u/healthcheck) for enabling HEALTHCHECK behavior in the official images.
These images are not maintained and are only provided as a reference in implementing your own HEALTHCHECK.

So if users want added functionality: healthcheck or otherwise then we try to demonstrate best practices such that users would have a reference for maintaining their own images for the specific functionality they want; as we try to maintain as close to upstream as possible to provide that base platform to build off of.

[EdwinHoksberg]

The healthcheck repo serves as an example for creating your own image derived from the healthcheck-prototypes provided.

Ah, I didn't even know that existed, I guess I'll close this then.