Naming and inspecting containers

Naming and inspecting containers

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 '' <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.)