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Multi-Stage builds allow you

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to have one Dockerfile,

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that define multiple build steps

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or setup steps, so called "stages" inside of that file.

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Stages can copy results from each other,

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so we can have one stage to create the optimized files

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and another stage to serve them.

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We can either build the entire Dockerfile

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going through all stages, step by step from top to bottom

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or we select individual stages up to which we wanna build,

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skipping all stages that would come after them

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that are multi-stage builds and multi-stage Dockerfiles.

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That's exactly what we can use here.

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You can think of this build step here as our first stage.

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We grab and install our dependencies,

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we grab our source code

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and then we build that source code

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with the code and the dependencies.

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After this step here, we have our finished source code.

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Now, with multistage builds,

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we just have to use "RUN" instead of command

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and therefore just "NPM run build" like this.

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Then we can continue with more steps thereafter.

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Now, we could do it as in a regular Dockerfile as well.

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But now here's the special thing,

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I wanna switch to a different base image after this command,

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Once we have these optimized files.

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Because we only need node to build the optimized files,

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because we need the NPM command,

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which ships together with node

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and because the build script actually also will use node

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under the hood.

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But once we get these optimized files,

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we don't need node anymore,

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unless we wanna bring our own node server

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to serve these files.

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But we don't need to do that,

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we could use nginx for that,

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which is a very lightweight and slim web server,

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which would totally serve our purposes here.

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I wanna switch to a different base image

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after this run command here.

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We can do this.

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We can have a second FROM statement here,

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effectively turning this

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into a multi-stage build Dockerfile.

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Because typically, you must only have one base image

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but you can indeed switch.

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In that case, this previous step you could say,

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will be discarded and you will switch to a new base image.

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Here, I wanna switch to nginx

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and there used the latest stable-alpine version,

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which again, is a very slim nginx version.

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You can look up these available tags

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on the nginx Docker Hub page, of course.

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Now here, we wanna do something special though,

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we don't want to have our previous changes be discarded.

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Instead, we wanna use the optimized files and serve them.

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Therefore, you can add a special instruction you could say,

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after this FROM instruction here,

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after every FROM instruction deed.

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You can add the AS keyword

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and give this any name of your choice,

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like for example build.

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But again, this name is up to you.

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Then here in our second stage,

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so on the second base image in this Dockerfile,

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we can copy from this first stage

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by using the special "dash dash from" option here

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on the copy instruction.

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Then you add an equal sign,

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and then the stage name from what you wanna copy,

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In this case, build.

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That means we'll copy the final content

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from that build stage.

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From all the instructions up to the next FROM instruction

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into this new stage here.

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Now of course, I don't wanna copy everything

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which is in this file system.

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After FROM build,

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you still need to specify the source path,

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just as you did it on copy before as well.

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Here we also copied from the local file system

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to the working directory inside of the container.

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Now here with the FROM option,

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we're telling Docker that this copy

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will not refer to our local host project folder,

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but instead queue the file system from this build stage.

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Now here, we can specify a path

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in that first build stage file system.

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I wanna use "app/build" because...

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That's something you need to know.

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The built command here in a React project

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will create a build folder

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which holds these final servable files.

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Therefore here I copied from the build stage,

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and data from the app/build folder.

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Now I wanna copy into the user.

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So usr/share/nginx/html folder

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here in my nginx image.

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That's a special folder for this nginx image.

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It is the default folder

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from where nginx will try to serve files.

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These are always things you can look up

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on your official image pages.

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They are you, for example,

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find that if you wanna host some simple static content,

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which is exactly what we have here,

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we just have an HTML file and a bunch of JavaScript files,

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which is static content.

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We just have to host the content

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of this user share nginx HTML folder.

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Therefore, that's the folder to which we copy here.

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Now we're using this multi-stage feature

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to copy the result from the first stage

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into this new stage.

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Now, the final container

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will only include that second stage,

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but it will first of all build this first stage

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to derive this final stage.

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You could also have more than one stage

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in one at the same Dockerfile.

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If you need that you can have as many stages

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as you want.

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For example, an extra stage for running your tests.

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Here however,

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I'm happy with copying this.

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But now I wanna expose Port 80

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because that is the default port nginx exposes internally

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so I wanna expose it here as well in my own image,

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which is based on nginx.

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Then the final command here at the end

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is that I wanna start ngnix.

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I want to start this nginx server

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and ask the official documentation states

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if we run it ourselves,

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we should add this "dash g, daemon off;" option here.

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Therefore, let's do that.

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Let's add "dash g, daemon off;"

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and don't forget this semicolon at the end.

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This is how we should start nginx if we started ourselves,

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which we wanna do here,

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since we wanna start it after we copied in our custom code.

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This is now a brand new feature of course.

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We haven't seen multi-stage Dockerfiles before,

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but it's a powerful feature,

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because it's great for situations like this,

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where we have an application which we can serve

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the way it is,

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but which we need to build first.

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Then a multi-stage build is of course awesome.

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Now, that we've learned about that

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and now that we've build our multi-stage Dockerfile,

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let's see how we would deploy that.