Naming and inspecting containers

Markings on container door
Figure 47 : Markings on container door

Objectives

In this lesson, we will learn about an important Docker concept: container naming.

Naming allows us to:

  • Reference easily a container.

  • Ensure unicity of a specific container.

We will also see the inspect command, which gives a lot of details about a container.

Naming our containers

So far, we have referenced containers with their ID.

We have copy-pasted the ID, or used a shortened prefix.

But each container can also be referenced by its name.

If a container is named thumbnail-worker, I can do:

$ docker logs thumbnail-worker
$ docker stop thumbnail-worker
etc.

Default names

When we create a container, if we don't give a specific name, Docker will pick one for us.

It will be the concatenation of:

  • A mood (furious, goofy, suspicious, boring...)

  • The name of a famous inventor (tesla, darwin, wozniak...)

Examples: happy_curie, clever_hopper, jovial_lovelace ...

Specifying a name

You can set the name of the container when you create it.

$ docker run --name ticktock jpetazzo/clock

If you specify a name that already exists, Docker will refuse to create the container.

This lets us enforce unicity of a given resource.

Renaming containers

  • You can rename containers with docker rename.

  • This allows you to "free up" a name without destroying the associated container.

Inspecting a container

The docker inspect command will output a very detailed JSON map.

$ docker inspect <containerID>
[{
...
(many pages of JSON here)
...

There are multiple ways to consume that information.

Parsing JSON with the Shell

  • You could grep and cut or awk the output of docker inspect.

  • Please, don't.

  • It's painful.

  • If you really must parse JSON from the Shell, use JQ! (It's great.)

$ docker inspect <containerID> | jq .
  • We will see a better solution which doesn't require extra tools.

Using --format

You can specify a format string, which will be parsed by Go's text/template package.

$ docker inspect --format '{{ json .Created }}' <containerID>
"2015-02-24T07:21:11.712240394Z"

  • The generic syntax is to wrap the expression with double curly braces.

  • The expression starts with a dot representing the JSON object.

  • Then each field or member can be accessed in dotted notation syntax.

  • The optional json keyword asks for valid JSON output.
    (e.g. here it adds the surrounding double-quotes.)