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Docker & dotnet - add WORKDIR to docker cmd #18043

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54 changes: 31 additions & 23 deletions docs/core/docker/build-container.md
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Original file line number Diff line number Diff line change
Expand Up @@ -164,7 +164,7 @@ myapp.deps.json myapp.dll myapp.pdb myapp.runtimeconfig.json

The *Dockerfile* file is used by the `docker build` command to create a container image. This file is a text file named *Dockerfile* that doesn't have an extension.

In your terminal, navigate up a directory to the working folder you created at the start. Create a file named *Dockerfile* in your working folder and open it in a text editor. Depending on the type of application you're going to containerize, you'll choose either the ASP.NET Core runtime or the .NET Core runtime. When in doubt, choose the ASP.NET Core runtime, which includes the .NET Core runtime. This tutorial will use the ASP.NET Core runtime image, but the application created in the previous sections is an .NET Core application.
In your terminal, navigate back one directory to the working folder you created at the start. Create a file named *Dockerfile* in your working folder and open it in a text editor. Depending on the type of application you're going to containerize, you'll choose either the ASP.NET Core runtime or the .NET Core runtime. When in doubt, choose the ASP.NET Core runtime, which includes the .NET Core runtime. This tutorial will use the ASP.NET Core runtime image, but the application created in the previous sections is an .NET Core application.

- ASP.NET Core runtime

Expand Down Expand Up @@ -214,42 +214,50 @@ Docker will process each line in the *Dockerfile*. The `.` in the `docker build`
```console
> docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
myimage latest 38db0eb8f648 4 weeks ago 346MB
mcr.microsoft.com/dotnet/core/aspnet 3.1 38db0eb8f648 4 weeks ago 346MB
myimage latest 54240314fe71 4 weeks ago 346MB
mcr.microsoft.com/dotnet/core/aspnet 3.1 54240314fe71 4 weeks ago 346MB
```

Notice that the two images share the same **IMAGE ID** value. The value is the same between both images because the only command in the *Dockerfile* was to base the new image on an existing image. Let's add two commands to the *Dockerfile*. Each command creates a new image layer with the final command representing the image the **myimage** repository entry points to.

```dockerfile
COPY app/bin/Release/netcoreapp3.1/publish/ app/

ENTRYPOINT ["dotnet", "app/myapp.dll"]
WORKDIR /app

ENTRYPOINT ["dotnet", "myapp.dll"]
```

The `COPY` command tells Docker to copy the specified folder on your computer to a folder in the container. In this example, the *publish* folder is copied to a folder named *app* in the container.

The `WORKDIR` command changes the **current directory** inside of the container to *app*.

The next command, `ENTRYPOINT`, tells Docker to configure the container to run as an executable. When the container starts, the `ENTRYPOINT` command runs. When this command ends, the container will automatically stop.

From your terminal, run `docker build -t myimage -f Dockerfile .` and when that command finishes, run `docker images`.

```console
> docker build -t myimage -f Dockerfile .
Sending build context to Docker daemon 1.624MB
Step 1/3 : FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
---> 38db0eb8f648
Step 2/3 : COPY app/bin/Release/netcoreapp3.1/publish/ app/
---> 37873673e468
Step 3/3 : ENTRYPOINT ["dotnet", "app/myapp.dll"]
---> Running in d8deb7b3aa9e
Removing intermediate container d8deb7b3aa9e
---> 0d602ca35c1d
Successfully built 0d602ca35c1d
Sending build context to Docker daemon 1.121MB
Step 1/4 : FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
---> 54240314fe71
Step 2/4 : COPY app/bin/Release/netcoreapp3.1/publish/ app/
---> 1e05ea8b3ef5
Step 3/4 : WORKDIR /app
---> Running in 8c8f710e6292
Removing intermediate container 8c8f710e6292
---> 31575599f7dc
Step 4/4 : ENTRYPOINT ["dotnet", "myapp.dll"]
---> Running in 93851322fb76
Removing intermediate container 93851322fb76
---> e496e8b22d02
Successfully built e496e8b22d02
Successfully tagged myimage:latest

> docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
myimage latest 0d602ca35c1d 4 seconds ago 346MB
mcr.microsoft.com/dotnet/core/aspnet 3.1 38db0eb8f648 4 weeks ago 346MB
myimage latest e496e8b22d02 4 seconds ago 346MB
mcr.microsoft.com/dotnet/core/aspnet 3.1 54240314fe71 4 weeks ago 346MB
```

Each command in the *Dockerfile* generated a layer and created an **IMAGE ID**. The final **IMAGE ID** (yours will be different) is **ddcc6646461b** and next you'll create a container based on this image.
Expand All @@ -260,15 +268,15 @@ Now that you have an image that contains your app, you can create a container. Y

```console
> docker create myimage
ceda87b219a4e55e9ad5d833ee1a7ea4da21b5ea7ce5a7d08f3051152e784944
9222af24353f42bab6c13e01a0a64ef2c915cad27bdc46ffa32380581de11e91
```

The `docker create` command from above will create a container based on the **myimage** image. The output of that command shows you the **CONTAINER ID** (yours will be different) of the created container. To see a list of *all* containers, use the `docker ps -a` command:

```console
> docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ceda87b219a4 myimage "dotnet app/myapp.dll" 4 seconds ago Created gallant_lehmann
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9222af24353f myimage "dotnet myapp.dll" 4 seconds ago Created gallant_lehmann
```

### Manage the container
Expand All @@ -282,8 +290,8 @@ The following example uses the `docker start` command to start the container, an
gallant_lehmann

> docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ceda87b219a4 myimage "dotnet app/myapp.dll" 7 minutes ago Up 8 seconds gallant_lehmann
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9222af24353f myimage "dotnet myapp.dll" 7 minutes ago Up 8 seconds gallant_lehmann
```

Similarly, the `docker stop` command will stop the container. The following example uses the `docker stop` command to stop the container, and then uses the `docker ps` command to show that no containers are running:
Expand Down Expand Up @@ -331,8 +339,8 @@ The following example lists all containers. It then uses the `docker rm` command

```console
> docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ceda87b219a4 myimage "dotnet app/myapp.dll" 19 minutes ago Exited gallant_lehmann
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9222af24353f myimage "dotnet myapp.dll" 19 minutes ago Exited gallant_lehmann

> docker rm gallant_lehmann
gallant_lehmann
Expand Down