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All.dind and sibling containers.how to guide

Docker-in-docker (dind)#

  • It is possible to install a Docker engine inside a Docker container so that one can run Docker container (e.g., OMS or IM) inside an isolated amp container.
  • The problems with this approach are:
    • Dind requires to run the external container in privileged mode, which might not be possible due to security concerns
    • The Docker / build cache is not shared across parent and children containers, so one needs to pull / build an image every time the outermost container is restarted
  • An alternative approach is the "sibling container" approach

Sibling container approach#

  • Refs:
  • Often what's really needed is the ability to build / run a container from another container (e.g., CI or unit test). This can be achieved by mounting the Docker socket /var/run/docker.sock to the container, so that a container can talk to Docker Engine.
  • This approach allows reuse of the build cache across the sibling containers.
  • The downside is less isolation from the external container, e.g., spawned containers can be left hanging or can collide.
  • E.g., 
    # Run `docker ps` in a container, showing the containers running in the main
container
> docker run -ti --rm \
            -v /var/run/docker.sock:/var/run/docker.sock \
            dindtest \
            docker ps

# Start a sibling hello world container:
> docker run -it --rm \
            -v /var/run/docker.sock:/var/run/docker.sock \
            dindtest \
            docker run -ti --rm hello-world

Connecting to Postgres instance using sibling containers#

  • We can start the Docker container with Postgres as a service from outside the container. 
    > (cd oms;  i oms_docker_up -s local)
INFO: > cmd='/local/home/gsaggese/src/venv/amp.client_venv/bin/invoke oms_docker_up -s local'
report_memory_usage=False report_cpu_usage=False
docker-compose \
--file /local/home/gsaggese/src/sasm-lime4/amp/oms/devops/compose/docker-compose.yml \
--env-file /local/home/gsaggese/src/sasm-lime4/amp/oms/devops/env/local.oms_db_config.env \
up \
oms_postgres
Creating compose_oms_postgres_1 ... done
Attaching to compose_oms_postgres_1
oms_postgres_1  |
oms_postgres_1  | PostgreSQL Database directory appears to contain a database; Skipping initialization
oms_postgres_1  |
oms_postgres_1  | 2022-05-19 22:57:15.659 UTC [1] LOG:  starting PostgreSQL 13.5 (Debian 13.5-1.pgdg110+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit
oms_postgres_1  | 2022-05-19 22:57:15.659 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
oms_postgres_1  | 2022-05-19 22:57:15.659 UTC [1] LOG:  listening on IPv6 address "::", port 5432
oms_postgres_1  | 2022-05-19 22:57:15.663 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
oms_postgres_1  | 2022-05-19 22:57:15.670 UTC [25] LOG:  database system was shut down at 2022-05-19 22:56:50 UTC
oms_postgres_1  | 2022-05-19 22:57:15.674 UTC [1] LOG:  database system is ready to accept connections
  • Note that Postgres needs to be
  • Start a container able to
  • From inside a container I launch postgres through the /var/... 
    > docker ps | grep postgres
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
83bba0818c74 postgres:13 "docker-entrypoint.s..." 6 minutes ago Up 6 minutes
0.0.0.0:5432->5432/tcp compose-oms_postgres-1
  • Test connection to the DB from outside the container 
    > psql --host=cf-spm-dev4 --port=5432 --user aljsdalsd -d oms_postgres_db_local
Password for user aljsdalsd:
psql (9.5.25, server 13.5 (Debian 13.5-1.pgdg110+1))
WARNING: psql major version 9.5, server major version 13.
                Some psql features might not work.
Type "help" for help.
oms_postgres_db_local=#
  • Test connection to the DB from inside the container 
    > psql --host=cf-spm-dev4 --port=5432 --user aljsdalsd -d oms_postgres_db_local
...