docker
/
docs
mirror of https://github.com/docker/docs.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Update get started part 7 (#16821) 

* Update get started part 7
This commit is contained in:
Craig Osterhout 2023-03-06 07:44:33 -08:00 committed by GitHub
parent 271fe6df6d
commit bc511bd942
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 76 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

132
get-started/07_multi_container.md
View File

@ -1,22 +1,20 @@
---
title: "Multi container apps"
keywords: get started, setup, orientation, quickstart, intro, concepts, containers, docker desktop
description: Using more than one container in our application
description: Using more than one container in your application
---
Up to this point, we have been working with single container apps. But, we now want to add MySQL to the
Up to this point, you've been working with single container apps. But, now you will add MySQL to the
application stack. The following question often arises - "Where will MySQL run? Install it in the same
container or run it separately?" In general, **each container should do one thing and do it well.** A few
reasons:
container or run it separately?" In general, each container should do one thing and do it well. The following are a few reasons to run the container separately:
- There's a good chance you'd have to scale APIs and front-ends differently than databases.
- Separate containers let you version and update versions in isolation.
- While you may use a container for the database locally, you may want to use a managed service
for the database in production. You don't want to ship your database engine with your app then.
- Running multiple processes will require a process manager (the container only starts one process),
which adds complexity to container startup/shutdown.
- Running multiple processes will require a process manager (the container only starts one process), which adds complexity to container startup/shutdown.
And there are more reasons. So, we will update our application to work like this:
And there are more reasons. So, like the following diagram, it's best to run your app in multiple containers.
![Todo App connected to MySQL container](images/multi-app-architecture.png)
{: .text-center }
@ -24,30 +22,34 @@ And there are more reasons. So, we will update our application to work like this
## Container networking
Remember that containers, by default, run in isolation and don't know anything about other processes
or containers on the same machine. So, how do we allow one container to talk to another? The answer is
**networking**. Now, you don't have to be a network engineer (hooray!). Simply remember this rule...
> **Note**
>
> If two containers are on the same network, they can talk to each other. If they aren't, they can't.
or containers on the same machine. So, how do you allow one container to talk to another? The answer is
networking. If you place the two containers on the same network, they can talk to each other.
## Start MySQL
There are two ways to put a container on a network:
1) Assign it at start or
2) connect an existing container.
For now, we will create the network first and attach the MySQL container at startup.
- Assign the network when starting the container.
- Connect an already running container to a network.
In the following steps, you'll create the network first and then attach the MySQL container at startup.
1. Create the network.
```console
$ docker network create todo-app
```
```console
$ docker network create todo-app
```
2. Start a MySQL container and attach it to the network. We're also going to define a few environment variables that the
database will use to initialize the database (see the "Environment Variables" section in the [MySQL Docker Hub listing](https://hub.docker.com/_/mysql/)).
2. Start a MySQL container and attach it to the network. You're also going to define a few environment variables that the
database will use to initialize the database. To learn more about the MySQL environment variables, see the "Environment Variables" section in the [MySQL Docker Hub listing](https://hub.docker.com/_/mysql/)).
```console
<ul class="nav nav-tabs">
<li class="active"><a data-toggle="tab" data-target="#mac-linux">Mac / Linux</a></li>
<li><a data-toggle="tab" data-target="#windows">Windows</a></li>
</ul>
<div class="tab-content">
<div id="mac-linux" class="tab-pane fade in active" markdown="1">
```console
$ docker run -d \
--network todo-app --network-alias mysql \
-v todo-mysql-data:/var/lib/mysql \
@ -56,7 +58,11 @@ For now, we will create the network first and attach the MySQL container at star
mysql:8.0
```
If you are using Windows then use this command in PowerShell.
<hr>
</div>
<div id="windows" class="tab-pane fade" markdown="1">
In Windows, run this command in PowerShell.
```powershell
$ docker run -d `
@ -67,19 +73,23 @@ For now, we will create the network first and attach the MySQL container at star
mysql:8.0
```
You'll also see we specified the `--network-alias` flag. We'll come back to that in just a moment.
<hr>
</div>
</div>
In the command above, you'll see the `--network-alias` flag. In a later section, you'll learn more about this flag.
> **Tip**
>
> You'll notice we're using a volume named `todo-mysql-data` here and mounting it at `/var/lib/mysql`, which is where MySQL stores its data. However, we never ran a `docker volume create` command. Docker recognizes we want to use a named volume and creates one automatically for us.
> You'll notice a volume named `todo-mysql-data` in the above command that is mounted at `/var/lib/mysql`, which is where MySQL stores its data. However, you never ran a `docker volume create` command. Docker recognizes you want to use a named volume and creates one automatically for you.
3. To confirm we have the database up and running, connect to the database and verify it connects.
3. To confirm you have the database up and running, connect to the database and verify that it connects.
```console
$ docker exec -it <mysql-container-id> mysql -u root -p
```
When the password prompt comes up, type in **secret**. In the MySQL shell, list the databases and verify
When the password prompt comes up, type in `secret`. In the MySQL shell, list the databases and verify
you see the `todos` database.
```console
@ -100,22 +110,22 @@ For now, we will create the network first and attach the MySQL container at star
+--------------------+
5 rows in set (0.00 sec)
```
Exit the MySQL shell to return to the shell on our machine.
4. Exit the MySQL shell to return to the shell on your machine.
```console
mysql> exit
```
Hooray! We have our `todos` database and it's ready for us to use!
You now have a `todos` database and it's ready for you to use.
## Connect to MySQL
Now that we know MySQL is up and running, let's use it! But, the question is... how? If we run
another container on the same network, how do we find the container (remember each container has its own IP
address)?
Now that you know MySQL is up and running, you can use it. But, how do you use it? If you run
another container on the same network, how do you find the container? Remember that each container has its own IP address.
To figure it out, we're going to make use of the [nicolaka/netshoot](https://github.com/nicolaka/netshoot) container,
which ships with a _lot_ of tools that are useful for troubleshooting or debugging networking issues.
To answer the questions above and better understand container networking, you're going to make use of the [nicolaka/netshoot](https://github.com/nicolaka/netshoot) container,
which ships with a lot of tools that are useful for troubleshooting or debugging networking issues.
1. Start a new container using the nicolaka/netshoot image. Make sure to connect it to the same network.
@ -123,14 +133,14 @@ which ships with a _lot_ of tools that are useful for troubleshooting or debuggi
$ docker run -it --network todo-app nicolaka/netshoot
```
2. Inside the container, we're going to use the `dig` command, which is a useful DNS tool. We're going to look up
2. Inside the container, you're going to use the `dig` command, which is a useful DNS tool. You're going to look up
the IP address for the hostname `mysql`.
```console
$ dig mysql
```
And you'll get an output like this...
You should get output like the following.
```text
; <<>> DiG 9.18.8 <<>> mysql
@ -153,11 +163,11 @@ which ships with a _lot_ of tools that are useful for troubleshooting or debuggi
In the "ANSWER SECTION", you will see an `A` record for `mysql` that resolves to `172.23.0.2`
(your IP address will most likely have a different value). While `mysql` isn't normally a valid hostname,
Docker was able to resolve it to the IP address of the container that had that network alias (remember the
`--network-alias` flag we used earlier?).
Docker was able to resolve it to the IP address of the container that had that network alias. Remember, you used the
`--network-alias` earlier.
What this means is... our app only simply needs to connect to a host named `mysql` and it'll talk to the
database! It doesn't get much simpler than that!
What this means is that your app only simply needs to connect to a host named `mysql` and it'll talk to the
database.
## Run your app with MySQL
@ -168,9 +178,9 @@ The todo app supports the setting of a few environment variables to specify MySQ
- `MYSQL_PASSWORD` - the password to use for the connection
- `MYSQL_DB` - the database to use once connected
> **Setting Connection Settings via Env Vars**
> **Note**
>
> While using env vars to set connection settings is generally ok for development, it is **HIGHLY DISCOURAGED**
> While using env vars to set connection settings is generally accepted for development, it's highly discouraged
> when running applications in production. Diogo Monica, a former lead of security at Docker,
> [wrote a fantastic blog post](https://diogomonica.com/2017/03/27/why-you-shouldnt-use-env-variables-for-secret-data/){:target="_blank" rel="noopener" class="_"}
> explaining why.
@ -183,14 +193,16 @@ The todo app supports the setting of a few environment variables to specify MySQ
> as the connection password. Docker doesn't do anything to support these env vars. Your app will need to know to look for
> the variable and get the file contents.
With all of that explained, let's start our dev-ready container!
You can now start your dev-ready container.
1. **Note**: for MySQL versions 8.0 and higher, make sure to include the following commands in `mysql`.
```console
mysql> ALTER USER 'root' IDENTIFIED WITH mysql_native_password BY 'secret';
mysql> flush privileges;
```
2. We'll specify each of the environment variables above, as well as connect the container to our app network.
1. Specify each of the environment variables above, as well as connect the container to your app network.
<ul class="nav nav-tabs">
<li class="active"><a data-toggle="tab" data-target="#mac-linux2">Mac / Linux</a></li>
<li><a data-toggle="tab" data-target="#windows2">Windows</a></li>
</ul>
<div class="tab-content">
<div id="mac-linux2" class="tab-pane fade in active" markdown="1">
```console
$ docker run -dp 3000:3000 \
@ -204,7 +216,11 @@ With all of that explained, let's start our dev-ready container!
sh -c "yarn install && yarn run dev"
```
If you are using Windows then use this command in PowerShell.
<hr>
</div>
<div id="windows2" class="tab-pane fade" markdown="1">
In Windows, run this command in PowerShell.
```powershell
$ docker run -dp 3000:3000 `
@ -217,7 +233,11 @@ With all of that explained, let's start our dev-ready container!
node:18-alpine `
sh -c "yarn install && yarn run dev"
```
3. If we look at the logs for the container (`docker logs -f <container-id>`), we should see a message indicating it's
<hr>
</div>
</div>
2. If you look at the logs for the container (`docker logs -f <container-id>`), you should see a message similar to the following, which indicates it's
using the mysql database.
```console
@ -230,10 +250,10 @@ With all of that explained, let's start our dev-ready container!
Listening on port 3000
```
4. Open the app in your browser and add a few items to your todo list.
3. Open the app in your browser and add a few items to your todo list.
5. Connect to the mysql database and prove that the items are being written to the database. Remember, the password
is **secret**.
4. Connect to the mysql database and prove that the items are being written to the database. Remember, the password
is `secret`.
```console
$ docker exec -it <mysql-container-id> mysql -p todos
@ -251,7 +271,7 @@ With all of that explained, let's start our dev-ready container!
+--------------------------------------+--------------------+-----------+
```
Obviously, your table will look different because it has your items. But, you should see them stored there!
Your table will look different because it has your items. But, you should see them stored there.
## Next steps
@ -263,6 +283,6 @@ this application. You have to create a network, start containers, specify all of
ports, and more! That's a lot to remember and it's certainly making things harder to pass along to someone else.
In the next section, you'll learn about Docker Compose. With Docker Compose, you can share your application stacks in a
much easier way and let others spin them up with a single (and simple) command!
much easier way and let others spin them up with a single, simple command.
[Use Docker Compose](08_using_compose.md){: .button .primary-btn}