I’m looking for a way to scale up a docker-compose service & saw the --scale option but could not find any method to get the index & count within each container.
Here’s a simplified compose file:
version: '2.1' services: my_thing: restart: always build: . entrypoint: /entry.sh depends_on: - database database: restart: always image: postgres:12.1-alpine ...
If I did
docker-compose up my_thing --scale 5 within the entry I’d like to be able
to see which instance I am (1 to 5) & how many instances there are in total (5 in this example).
I need this as the API ‘my_thing’ connects to needs this information to delegate events to each instance.
For example my entry could be
echo "Hello I'm container $index of $count";
& then when I run
docker-compose up my_thing --scale 5 (note that I’d prefer not to hard-code the the count)
Then each container would respectively run the entry & output:
Hello I'm container 1 of 5 Hello I'm container 2 of 5 Hello I'm container 3 of 5 ... and so on
If any container crashed I’d like it restarted knowing it’s index.
Is this possible or do I need to figure out some alternative or build my own tooling?
If there’s any example of how to do something like this with docker swarm that may help too.