docker_cheat_sheet.markdown

Table of Contents

• Cheat sheet
  • Refer container by ID
  • SSH into a container
  • Run psql

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Cheat sheet

Refer container by ID

To avoid excessive typing or copy-pasting when running Docker commands, you can refer to a container by only a part of its ID:

# PostgreSQL container has an ID "72bfc559a72b"
$ docker ps -a
CONTAINER ID        IMAGE                                       COMMAND
72bfc559a72b        gcr.io/mcback/postgresql-server:latest   "/opt/mediacloud/bin…"

# ...but we can refer to it using only a part of the ID ("72b")
$ docker inspect 72b
[
    {
        "Id": "72bfc559a72b88a88262c3717e4406e36b4d86730bf22f2dcbba5046edd473f2",
        "Created": "2019-06-12T16:47:15.1030581Z",
        # ...
    }
]

SSH into a container

Given that behind the scenes a container is just a fancy chroot, it wouldn't make much sense to SSH into it because that would amount to you SSHing into your own machine. Instead, you can use one of the following commands:

• To run bash in a running container:

  1. Find out running container's ID:

     $ docker ps
     CONTAINER ID        IMAGE                           COMMAND
     <...>
     b519dab9d10b        gcr.io/mcback/<...>:latest   "important_research.sh"

  2. Run docker exec -it <container_id_or_just_a_part_of_it> bash:

     $ docker exec -it b5 bash
     mediacloud@b519dab9d10b:/$

     Docker will start an interactive bash session in addition to container's main command (important_research.sh in this case).

• To start a new container and run bash instead of image's default command:

  1. Run docker run -it --entrypoint=bash <image_name>:

     $ docker run -it --entrypoint=bash gcr.io/mcback/tools:latest
     mediacloud@f5a121fe5907:/$ 

• To run bash in a stopped container, either:

  1. docker start it first and then run docker exec as detailed above, or
  2. Export the stopped container to an image with docker commit and then start a new container from said image as detailed here

Run psql

To access PostgreSQL directly, you can either run psql in a postgresql-server container, or map the port from a PostgreSQL container to your host machine and access it from there:

• To run psql in PostgreSQL container:

  1. Find out container ID of a running PostgreSQL's container:

     $ docker ps | grep postgres
     CONTAINER ID        IMAGE                                       COMMAND
     29ad7542c5fe        gcr.io/mcback/postgresql-server:latest   "/opt/mediacloud/bin…"

  2. Execute psql in a running PostgreSQL container:

     $ docker exec -it 29a psql
     psql (13.3 (Ubuntu 11.3-1.pgdg20.04+1))
     Type "help" for help.
     
     mediacloud=# 

• To run psql on your host machine:

  1. Make sure that nothing is listening on the host machine's port to which you're about to bind the container's port;

  2. Add a port mapping before you start a new PostgreSQL container:

     • If you're running a standalone PostgreSQL container, add a port mapping by adding -p [host_bind_ip:]host_port:container_port argument to docker run:

       $ docker run -d -p "127.0.0.1:5432:5432" gcr.io/mcback/postgresql-server:latest

     • If you're running PostgreSQL container as part of a (testing) Docker Compose environment, add a port mapping by defining ports: directive to docker-compose.tests.yml:

       version: "3.7"
       
       services:
       
          # <...>
          
           postgresql-server:
               image: gcr.io/mcback/postgresql-server:latest
               # <...>
               ports:
                   # "[host_bind_ip:]host_port:container_port"
                   - "127.0.0.1:5432:5432"

       and then start the whole Compose environment with -m (--map_ports) argument to run.py:

       $ ./dev/run.py -m common bash

  3. After starting either a standalone PostgreSQL container or a Compose environment with PostgreSQL as one of the services in it, container's port should be mapped to the host machine as defined either in -p argument to docker run or ports: section in docker-compose.tests.yml:

     $ docker ps | grep postg
     CONTAINER ID        IMAGE                                       PORTS
     72bfc559a72b        gcr.io/mcback/postgresql-server:latest   127.0.0.1:5432->5432/tcp

     and you should be able to connect to the container from your host machine as you would with any other PostgreSQL instance:

     $ psql -h localhost -U mediacloud -d mediacloud
     Password for user mediacloud: 
     Timing is on.
     Expanded display is on.
     psql (13.3)
     Type "help" for help.
     
     mediacloud=#