Docker Healthchecks

[JerboaGobi]

I was wondering if there are any plans to add health checks? I've attempted to add them myself through docker-compose but the image doesn't contain binaries that can be used to perform a useful health check or at least none that my brain could think of.

[ShreyasZare]

By health checks if you mean to do health check for two or more web servers such that the DNS server returns IP addresses only for the ones that are online, then there is a Failover app that you can use to configure your zone.

[JerboaGobi]

Health checks for the Docker image. Something that checks and verifies the container booted properly. Top the service, curl or netcat the DNS ports.

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

[ShreyasZare]

Thanks for point that out. Will check it.

[kevdogg]

If wget was installed in the container by default, you could use something like:
wget --no-check-certificate --no-verbose --tries=3 --spider http://localhost:5380 || exit 1
as the healthcheck. This could be modified within a docker compose with a different port/protocol if https was employed. Just a suggestion. Works for me when adding wget in a Dockerfile and adding this as a healthcheck within docker-compose.

[ShreyasZare]

@kevdogg there is even a better way to do this using dig command that is installed by default. You can check out this issue #1102 to see how it can be done.

[kevdogg]

Hey based on your post I tried the following (just to prove things were working since I received silent output) and it looks like the healthcheck actually worked (Great post btw)!!:

dig +short +retry=0 +norecurse @127.0.0.1 cloudflare.com || echo "1" && echo "0"

Neat!

So to just sum things up for anyone else, this is how I write my docker-compose.yml file for the healthcheck:
And in case anyone asking about the & and * stanzas, its a yaml anchors and aliases thing modified for docker compose files:
https://docs.docker.com/reference/compose-file/fragments/

---

x-healthcheck-parameters: &healthcheck-parameters
  interval: "30s"
  timeout: "3s"
  start_period: "5s"
  retries: 3

x-technitium-healthcheck: &technitium-healthcheck
  test: dig +short +retry=0 +norecurse @127.0.0.1 cloudflare.com || exit 1 && exit 0
  <<: *healthcheck-parameters

  dns-server:
    container_name: dns-server
    hostname: ns1.<domain>.com
    image: technitium/dns-server:latest
    restart: always
    healthcheck:
      <<: *technitium-healthcheck
    networks:
      - net
   ...