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If you have two applications and one database in a stack then the docker-compose.yml file looks like this

version: "3.3"

services:
  app1:
    image: custom-image-app1
    ports:
      - "8000:8000"
  app2:
    image: custom-image-app2
    ports:
      - "8080:8080"
  db:
    image: postgres:17
    environment:
      POSTGRES_DB: mydatabase
      POSTGRES_USER: myuser
      POSTGRES_PASSWORD: mypassword
    ports:
      - "5432:5432"

Let's say you have an update only in one application. How do you update the stack? If you run

docker stack down my_stack
docker build . -t my-app
docker stack up -c docker-compose.yml my_stack

then you are doing everything wrong!

After building a new image (or pulling it from the registry) you can update only the specific service with this command

docker service update --force --update-parallelism 1 --update-delay 5s my_stack_app1

But if you only need to add an environment variable

docker service update --env-add ALLOWED_HOSTS=mastodon my_stack_app1
# and verify that it's there
docker service inspect --format "{{ .Spec.TaskTemplate.ContainerSpec.Env }}" my_stack_app1

About logs

Check logs like this

docker service logs -f my_stack_app1

Set log rotation by editing /etc/docker/daemon.json

{
  "log-driver": "local",
  "log-opts": {
    "max-size": "10m"
  }
}

Reference: https://docs.docker.com/config/containers/logging/local/

You can check if the logs grow abundantly on your drive1

du -h $(docker inspect --format='{{.LogPath}}' $(docker ps -qa))

And possibly then archive them

docker inspect --format='{{.LogPath}}' $(docker ps -qa) | xargs -I{} sh -c 'gzip -c "{}" > "./$(basename "{}").gz"'

And delete... (careful one by one version)

sudo sh -c 'echo "" > $(docker inspect --format="{{.LogPath}}" e430578d8809)'

But do not do this type of deletion! It will break the output from the log command. You could still read logs from raw JSON:

sudo tail -n 50 -f /var/lib/docker/containers/e430578d8809005f7756606fc8e765a88813f1b17a59e23b19c8320758d70f46/e430578d8809005f7756606fc8e765a88813f1b17a59e23b19c8320758d70f46-json.log | jq -j '.["log"]'

I even managed to make a combined version when in a docker stack one service has several instnaces (search by the service name)

tail -qf $(docker inspect --format="{{.LogPath}}" $(sudo docker ps -f name=<your service name> -q)) | jq -j '.["log"]'

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