Red Green Repeat Adventures of a Spec Driven Junkie

Can I do Better: Connecting to Docker Containers

I like to improve my work flow by asking: “Can I do it better?” and see where that leads.

This time, I will walk you through a situation I encounter in a daily basis: connecting to a running Docker container and the show solution I use to turn a four step manual process into a single line.

If you are connecting to Docker containers frequently, this solution can help you be more efficient and focus on more important parts of the problem.

This article will take you less than three minutes to read.

Luster Bowl with Winged Horse source and more information

Introduction

I connect to running containers to do work or debug. The command I use connect to a container is:

% docker exec -it <container SHA> <command>

Before executing this command, I need to look up the container SHA. I don’t know what the container SHA is, it could be the same as the last time I connected to it, or it could be different.

To look up the container’s SHA, I run docker ps to list all the running containers and their SHA. Find the container running the image I want, say foo, take that SHA value and execute the above command.

Step by step of the above with details to connect to foo:

  1. Get a list of running containers running command: sudo docker ps

     $ docker ps
     CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
     b8996065500e        ubuntu              "/bin/bash"              4 seconds ago       Up 2 seconds                            clever_goldstine
     5bb3e80c076d        nginx:latest        "nginx -g 'daemon of…"   About a minute ago   Up About a minute   80/tcp              objective_hermann.1.6agqbzmx8qiazhwwncdegknwa
     f8ead854815d        registry:latest     "/entrypoint.sh /etc…"   44 seconds ago      Up 42 seconds       5000/tcp            registry.1.4efrmjz58hqjdtmhdqhpg4q0z
     v
     2df0bba15bc6        foo               "nginx -g 'daemon ..."   47 seconds ago      Up 46 seconds       80/tcp              sad_boyd
    
  2. From that list, pick out line running image named ‘foo’

     2df0bba15bc6        foo               "nginx -g 'daemon ..."   47 seconds ago      Up 46 seconds       80/tcp              sad_boyd
    
  3. From that line, pick out the container’s SHA

     2df0bba15bc6
    
  4. Remember container SHA, connect to container using original command.

     % sudo docker exec -it 2df0bba15bc6 bash
    

Isn’t this simple?

Honestly, it was, and then it got tedious after the n-th time, where n is greater than ten. Especially at the wee-hours and I need to get something done and go to bed.

It’s easy to fat finger the container SHA in the last command, causing more grief. Copy/paste is nice, but I still need to target the right SHA to copy.

In this process, there are four extra steps between logging in to host and goal of doing work in container (and sometimes: going to bed!)

Can I do better?

After the n+1 time, I figured out a better way, much better way. This is my solution to connect to container named ‘foo’ and run bash:

$ sudo docker exec -it $(sudo docker ps | grep foo | awk '{ print $1 }') bash

Explanation of key parts:

$() executes another command within a command - using that result in place
| passes output from left command as input into right command
grep grabs line that only match ‘foo’
awk picks out the first ($1) column and uses that

Whenever I need to connect to a docker container named ‘foo’, I just run the above command after logging in.

There’s no:

  • copying
  • fat fingering
  • more than one step needed

This command is easier to run in the wee-hours than the previous method. I can get in and out of a docker container easily.

Added benefit: it’s easy to find this command in the bash history (or make an alias!).

Conclusion

Instead of continuing to accept a four-step process in my work flow, asking “Can I do better?” dramatically reduced the process into a single line. Letting me work on more important items while connected to a Docker container.

Is there a multi-step process in your life that you ask: “Can I do better?” If there is and you can’t find a way to make it better, please contact me. I would love to see if we can solve it together.