Naming and inspecting containers

See also

• https://avril2018.container.training/intro.yml.html#231

• https://avril2018.container.training/intro.yml.html#10

• Les conseils et formations de Jérôme Petazzoni

Contents

• Naming and inspecting containers

  • Objectives

  • Naming our containers

  • Default names

  • Specifying a name

  • Renaming containers

  • Inspecting a container

  • Parsing JSON with the Shell

  • Using –format

Objectives

See also

• https://avril2018.container.training/intro.yml.html#233

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

See also

• https://avril2018.container.training/intro.yml.html#234

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

See also

• https://avril2018.container.training/intro.yml.html#235

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

See also

• https://avril2018.container.training/intro.yml.html#236

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

See also

• https://avril2018.container.training/intro.yml.html#237

You can rename containers with docker rename. This allows you to “free up” a name without destroying the associated container.

Inspecting a container

See also

• https://avril2018.container.training/intro.yml.html#238

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

See also

• https://avril2018.container.training/intro.yml.html#239

• 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

See also

• https://avril2018.container.training/intro.yml.html#240

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.)