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[WIP] Update basic docker guidance #2929

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[WIP] Update basic docker guidance #2929

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25a9c41
Update ruby docker version to 2.7.2
huwd Jan 18, 2021
19c6b6e
Small improvements to intro to Docker
huwd Jan 18, 2021
4f2f909
Fix postgres in docker now requires a POSTGRES_PASSWORD
huwd Jan 19, 2021
6a69f33
Add clarifying comment to explain container ID and the unusual name
huwd Jan 19, 2021
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37 changes: 25 additions & 12 deletions source/manual/intro-to-docker.html.md
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Expand Up @@ -29,20 +29,24 @@ Before you start, make sure you:

```shell
$mac docker --version
Docker version 18.09.2, build 6247962
Docker version <version number>, build <build>
```

The [Docker Engine release notes](https://docs.docker.com/engine/release-notes/) list the latest version number.

### Images and containers

* Run from the root of the [content-publisher] project:

```shell
$mac docker run -it ruby:2.6.3 bash
$mac docker run -it ruby:2.7.2 bash
```

`ruby:2.6.3` is the "image" that we specify. Using object oriented programming as an analogy, an image is like a "class". When we "instantiate" an instance of a class, these are called "containers".
`ruby:2.7.2` is the "image" that we specify. Using object oriented programming as an analogy, an image is like a "class". When we "instantiate" an instance of a class, these are called "containers".

The `ruby:2.7.2` image we are using is a debian system with Ruby pre-installed. Images are downloaded from the [Docker Registry][docker-registry]. The `bash` argument at the end will execute this inside the container, which means we get a bash shell.

The `ruby:2.6.3` image we are using is a debian system with Ruby pre-installed. Images are downloaded from the [Docker Registry][docker-registry]. The `bash` argument at the end will execute this inside the container, which means we get a bash shell.
You can leave the shell by typing `exit`.

What are the flags?

Expand All @@ -59,7 +63,7 @@ $mac docker run --help
* Mount your current directory as a volume to the container by running:

```shell
$mac docker run -it -v $(pwd):/app ruby:2.6.3 bash
$mac docker run -it -v $(pwd):/app ruby:2.7.2 bash
```

This will map your current directory (the root of the [content-publisher] project) to `/app` inside of the container. So now the files on your `$mac` for [content-publisher] are now also available inside of the container.
Expand All @@ -71,7 +75,7 @@ $dev cd /app
$dev bundle install
```

> Note: you may need to use a different image (e.g. `ruby:2.6.5`) depending on the version specified in [`.ruby-version`][content-publisher-ruby] in [content-publisher].
> Note: you may need to use a different image (e.g. `ruby:2.7.2`) depending on the version specified in [`.ruby-version`][content-publisher-ruby] in [content-publisher].
>
> Note: this may take a while, so feel free to stop it by pressing Ctrl+c as the next step will show why it doesn't matter at this point.

Expand All @@ -94,7 +98,7 @@ $mac docker volume create content-publisher-bundle
* Run docker with that volume by using the `-v` flag and passing it the name of the volume:

```shell
$mac docker run -it -v $(pwd):/app -v content-publisher-bundle:/usr/local/bundle ruby:2.6.3 bash
$mac docker run -it -v $(pwd):/app -v content-publisher-bundle:/usr/local/bundle ruby:2.7.2 bash
```

* Then install the gems again:
Expand All @@ -116,7 +120,7 @@ $dev bundle exec rake

We get an error: “could not find javascript runtime” - we need Node installed on our container. We can try to install Node here, but this won't persist and we'll have the same problem that we had above with installing gems.

Unlike gems, our install of Node won't need to change in the foreseeable future. It would be nice if our `ruby:2.6.3` image had it as well. We can't change the `ruby:2.6.3` image, but we can create our own image based off it.
Unlike gems, our install of Node won't need to change in the foreseeable future. It would be nice if our `ruby:2.7.2` image had it as well. We can't change the `ruby:2.7.2` image, but we can create our own image based off it.

### Create ruby + node image

Expand All @@ -133,7 +137,7 @@ Create a Dockerfile in the content-publisher project:
* Create a `Dockerfile` in the root of the [content-publisher] project:

```docker
FROM ruby:2.6.3
FROM ruby:2.7.2

RUN curl -sL https://deb.nodesource.com/setup_12.x | bash
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
Expand Down Expand Up @@ -200,7 +204,15 @@ Docker containers are quick to start and it's possible for them to talk to each
* In another terminal, run the following to start a new container based on the `postgres` image:

```shell
$mac docker run -it postgres
$mac docker run -e POSTGRES_PASSWORD=password -it postgres
```

Before it starts Postgres will check if a password is set. If do not supply a password `docker run` will print an error and fail to start the container. Postgres can set this password with an environment variable. We can supply this to docker with the `-e` flag.

```shell
$mac docker run --help
...
-e, --env list Set environment variables
```

* Now to see what containers you have, in another terminal run:
Expand All @@ -210,10 +222,11 @@ $mac docker ps

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a7b87be3e1bc postgres "docker-entrypoint.s…" 21 minutes ago Up 21 minutes 5432/tcp jovial_matsumoto
...
```

This shows us that `a7b87be3e1bc` or "jovial_matsumoto" is up and running. We can "inspect" the configuration of the container and get its IP, which we can use in the content-publisher container.
When containers spin up they are assigned an ID, in this case `a7b87be3e1bc`. Containers also have name. If you do not supply one it will default to a random one, in this case `jovial_matsumoto`.

We can see from running `docker ps` that `a7b87be3e1bc` or "jovial_matsumoto" is up and running. We can "inspect" the configuration of the container and get its IP, which we can use in the content-publisher container.

* Find the ID for the postgres container, and with it run:

Expand Down