Feature request: add HEALTHCHECK

[rnavarropiris]

Docker supports defining a command to determine if the container is running as intended (healthy), broken for some reason (unhealthy) or still initializing (starting):

• https://docs.docker.com/engine/reference/builder/#healthcheck

Adding this to this image with the semantic "the redis store is online and functional" would be quite nice.

Since the last HEALTHCHECK defined by a Dockerfile is the one actually used, images based on this one could define their own healthcheck without "interference" by the one provided by the redis image.

[rturk]

This can be really helpful when running this image in a Kubernetes cluster

[yosifkit]

Copying comment from docker-library/cassandra#76 (comment)

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

• users will have their own idea of what is "healthy"
• it does not actually test that the service is listening to connections outside of localhost (see https://github.com/docker-library/healthcheck for some examples that do more than what's proposed here, including attempting to check whether the service is listening remotely)
  • some of the Official Images even purposely start in a localhost only mode for database initialization and then kill and start the main service with full network availability
• after upgrading their images, current users will have extra unexpected load on their systems for healthchecks they don't necessarily need/want and may be unaware of

[rturk]

@yosifkit humbly disagree with your comment, any service should report if can perform what is expected/required to do.

[rnavarropiris]

@yosifkit
I also disagree, please see this comment

[tiredpixel]

@yosifkit, I also respectfully disagree. Please see my comment docker-library/postgres#282 (comment).

[paulotruta]

@yosifkit , I can see the point, but also disagree with this. Docker provides this, and Kubernetes cluster maintainers use this to have basic health check capabilities with their deploys.

[wglambert]

Copying comment from docker-library/cassandra#76 (comment)

I still don't think healthchecks should be added to official images.

• the docker defined ones are disabled when using kubernetes (Disable Docker's health check until we officially support it kubernetes/kubernetes#50796) since it conflicts with their own liveness and readiness probes
• they do not require a custom Dockerfile and can be defined in the docker-compose.yml (or stack.yml for swarm)
  • some example healthchecks are provided in the aforementioned https://github.com/docker-library/healthcheck
• sometimes systems are slow and a default healthcheck could kill the container early and prevent the system from ever properly initializing (Detecting container initialization on DATADIR is fragile docker-library/mysql#439)

[tianon]

Indeed, see also https://github.com/docker-library/faq#healthcheck.

[tgross35]

Very late to the party but for anyone from the future -

In general I feel that healthchecks shouldn't be enabled by default. However, it certainly isn't a bad idea to provide and document a good basic healthcheck (script included in image, command, etc) - something along the lines of "the running service considers itself to be healthy if X, and 80%+ of users would probably agree".

We're in luck; redis already has this. The following compose tidbit works well:

healthcheck:
    test: ["CMD", "redis-cli", "ping"]
    timeout: 10s
    retries: 3
    start_period: 10s

The command returns PONG if the ping successfully connects. Won't catch everything but is at least enough to report that redis is up and running.