What is the alternative to condition form of depends_on in docker-compose Version 3?
Solution 1:
There's been a move away from specifying container dependencies in compose. They're only valid at startup time and don't work when dependent containers are restarted at run time. Instead, each container should include mechanism to retry to reconnect to dependent services when the connection is dropped. Many libraries to connect to databases or REST API services have configurable built-in retries. I'd look into that. It is needed for production code anyway.
Solution 2:
From 1.27.0, 2.x and 3.x are merged with COMPOSE_SPEC schema.
version is now optional. So, you can just remove it and specify a condition as before:
services:
web:
build: .
depends_on:
redis:
condition: service_healthy
redis:
image: redis
healthcheck:
test: ["CMD", "redis-cli", "ping"]
interval: 1s
timeout: 3s
retries: 30
Solution 3:
There are some external tools that let you mimic this behaviour. For example, with the dockerize tool you can wrap your CMD
or ENTRYPOINT
with dockerize -wait
and that will prevent running your application until specified services are ready.
If your docker-compose file used to look like this:
version: '2.1'
services:
kafka:
image: spotify/kafka
healthcheck:
test: nc -z localhost 9092
webapp:
image: foo/bar # your image
healthcheck:
test: curl -f http://localhost:8080
tests:
image: bar/foo # your image
command: YOUR_TEST_COMMAND
depends_on:
kafka:
condition: service_healthy
webapp:
condition: service_healthy
then you can use dockerize
in your v3
compose file like this:
version: '3.0'
services:
kafka:
image: spotify/kafka
webapp:
image: foo/bar # your image
tests:
image: bar/foo # your image
command: dockerize -wait tcp://kafka:9092 -wait web://webapp:8080 YOUR_TEST_COMMAND
Solution 4:
Just thought I'd add my solution for when running postgres and an application via docker-compose where I need the application to wait for the init sql script to complete before starting.
dockerize seems to wait for the db port to be available (port 5432) which is the equivilant of depends_on
which can be used in docker 3:
version: '3'
services:
app:
container_name: back-end
depends_on:
- postgres
postgres:
image: postgres:10-alpine
container_name: postgres
ports:
- "5432:5432"
volumes:
- ./docker-init:/docker-entrypoint-initdb.d/
The Problem:
If you have a large init script the app will start before that completes as the depends_on
only waits for the db port.
Although I do agree that the solution should be implemented in the application logic, the problem we have is only for when we want to run tests and prepopulate the database with test data so it made more sense to implement a solution outside the code as I tend not like introducing code "to make tests work"
The Solution:
Implement a healthcheck on the postgres container.
For me that meant checking the command of pid 1 is postgres
as it will be running a different command on pid 1 while the init db scripts are running
Write a script on the application side which will wait for postgres
to become healthy
. The script looks like this:
#!/bin/bash
function check {
STATUS=\`curl -s --unix-socket /var/run/docker.sock http:/v1.24/containers/postgres/json | python -c 'import sys, json; print json.load('sys.stdin')["State"]["Health"]["Status"]'\`
if [ "$STATUS" = "healthy" ]; then
return 0
fi
return 1
}
until check; do
echo "Waiting for postgres to be ready"
sleep 5
done
echo "Postgres ready"
Then the docker-compose should mount the directories of the scripts so that we don't edit the Dockerfile for the application and if we're using a custom postgres image, this way we can continue to use the docker files for your published images.
We're also overriding the entry point defined in the docker file of the app so that we can run the wait script before the app starts
version: '3'
services:
app:
container_name: back-end
entrypoint: ["/bin/sh","-c","/opt/app/wait/wait-for-postgres.sh && <YOUR_APP_START_SCRIPT>"]
depends_on:
- postgres
volumes:
- //var/run/docker.sock:/var/run/docker.sock
- ./docker-scripts/wait-for-postgres:/opt/app/wait
postgres:
image: postgres:10-alpine
container_name: postgres
ports:
- "5432:5432"
volumes:
- ./docker-init:/docker-entrypoint-initdb.d/
- ./docker-scripts/postgres-healthcheck:/var/lib
healthcheck:
test: /var/lib/healthcheck.sh
interval: 5s
timeout: 5s
retries: 10