Docker - check if postgres is ready

Here is a shell one liner using pg_isready tool provided by PostgreSQL.

To call outside docker:

DOCKER_CONTAINER_NAME="mypgcontainer"timeout 90s bash -c "until docker exec $DOCKER_CONTAINER_NAME pg_isready ; do sleep 5 ; done"

Based on a post from Jeroma Belleman.

I tried wait-for-it, but it may be a problem to run it in docker container as in the docker image may not be installed nc (sometimes there is not even ping, telnet, curl..). So to check if the DB is up and running I have used HealthCheck in docker compose file what was checking return value of pg_isready, what is part of postgres database, so you do not need to install anything into docker images:

version: '2.3'services:  postgres-db:    image: postgresImage    healthcheck:      test: /usr/bin/pg_isready      interval: 5s      timeout: 10s      retries: 120    ports:      - '5432:5432'  aplication:    image: applicationImage    depends_on:      postgres-db:        condition: service_healthy

We solve this with a simple TCP check on port 5432, without any PG tooling. We just use wait-for-it.sh, and it works well. Postgres does not open the port until the server is actually ready to serve, so this is apparently fine.

Sample Dockerfile: https://github.com/apim-haufe-io/wicked.kong/blob/master/Dockerfile

Corresponding start script (only the last line is interesting for this specific problem): https://github.com/apim-haufe-io/wicked.kong/blob/master/startup.sh

Snippet:

wait-for-it.sh -h $KONG_PG_HOST -p 5432 -t 30 -- kong start --run-migrations

Wait for it: https://github.com/vishnubob/wait-for-it