---
description: Keeping your images small with multi-stage images
keywords: images, containers, best practices, multi-stage, multistage
title: Use multi-stage builds
redirect_from:
- /engine/userguide/eng-image/multistage-build/
---

Multistage builds are useful to anyone who has struggled to optimize Dockerfiles
while keeping them easy to read and maintain.

> **Acknowledgment**:
> Special thanks to [Alex Ellis](https://twitter.com/alexellisuk) for granting
> permission to use his blog post
> [Builder pattern vs. Multi-stage builds in Docker](https://blog.alexellis.io/mutli-stage-docker-builds/)
> as the basis of the examples below.

## Before multi-stage builds

One of the most challenging things about building images is keeping the image
size down. Each instruction in the Dockerfile adds a layer to the image, and you
need to remember to clean up any artifacts you don't need before moving on to
the next layer. To write a really efficient Dockerfile, you have traditionally
needed to employ shell tricks and other logic to keep the layers as small as
possible and to ensure that each layer has the artifacts it needs from the
previous layer and nothing else.

It was actually very common to have one Dockerfile to use for development (which
contained everything needed to build your application), and a slimmed-down one
to use for production, which only contained your application and exactly what
was needed to run it. This has been referred to as the "builder
pattern". Maintaining two Dockerfiles is not ideal.

Here's an example of a `Dockerfile.build` and `Dockerfile` which adhere to the
builder pattern above:

**`Dockerfile.build`**:

```dockerfile
FROM golang:1.7.3
WORKDIR /go/src/github.com/alexellis/href-counter/
COPY app.go .
RUN go get -d -v golang.org/x/net/html \
  && CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .
```

Notice that this example also artificially compresses two `RUN` commands together
using the Bash `&&` operator, to avoid creating an additional layer in the image.
This is failure-prone and hard to maintain. It's easy to insert another command
and forget to continue the line using the `\` character, for example.

**`Dockerfile`**:

```dockerfile
FROM alpine:latest  
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY app .
CMD ["./app"]  
```

**`build.sh`**:

```bash
#!/bin/sh
echo Building alexellis2/href-counter:build

docker build --build-arg https_proxy=$https_proxy --build-arg http_proxy=$http_proxy \  
    -t alexellis2/href-counter:build . -f Dockerfile.build

docker container create --name extract alexellis2/href-counter:build  
docker container cp extract:/go/src/github.com/alexellis/href-counter/app ./app  
docker container rm -f extract

echo Building alexellis2/href-counter:latest

docker build --no-cache -t alexellis2/href-counter:latest .
rm ./app
```

When you run the `build.sh` script, it needs to build the first image, create
a container from it to copy the artifact out, then build the second
image. Both images take up room on your system and you still have the `app`
artifact on your local disk as well.

Multi-stage builds vastly simplify this situation!

## Use multi-stage builds

With multi-stage builds, you use multiple `FROM` statements in your Dockerfile.
Each `FROM` instruction can use a different base, and each of them begins a new
stage of the build. You can selectively copy artifacts from one stage to
another, leaving behind everything you don't want in the final image. To show
how this works, let's adapt the Dockerfile from the previous section to use
multi-stage builds.

**`Dockerfile`**:

```dockerfile
FROM golang:1.7.3
WORKDIR /go/src/github.com/alexellis/href-counter/
RUN go get -d -v golang.org/x/net/html  
COPY app.go .
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .

FROM alpine:latest  
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY --from=0 /go/src/github.com/alexellis/href-counter/app .
CMD ["./app"]  
```

You only need the single Dockerfile. You don't need a separate build script,
either. Just run `docker build`.

```bash
$ docker build -t alexellis2/href-counter:latest .
```

The end result is the same tiny production image as before, with a
significant reduction in complexity. You don't need to create any intermediate
images and you don't need to extract any artifacts to your local system at all.

How does it work? The second `FROM` instruction starts a new build stage with
the `alpine:latest` image as its base. The `COPY --from=0` line copies just the
built artifact from the previous stage into this new stage. The Go SDK and any
intermediate artifacts are left behind, and not saved in the final image.

## Name your build stages

By default, the stages are not named, and you refer to them by their integer
number, starting with 0 for the first `FROM` instruction. However, you can
name your stages, by adding an `AS <NAME>` to the `FROM` instruction. This
example improves the previous one by naming the stages and using the name in
the `COPY` instruction. This means that even if the instructions in your
Dockerfile are re-ordered later, the `COPY` doesn't break.

```dockerfile
FROM golang:1.7.3 AS builder
WORKDIR /go/src/github.com/alexellis/href-counter/
RUN go get -d -v golang.org/x/net/html  
COPY app.go    .
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .

FROM alpine:latest  
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY --from=builder /go/src/github.com/alexellis/href-counter/app .
CMD ["./app"]  
```

## Stop at a specific build stage

When you build your image, you don't necessarily need to build the entire
Dockerfile including every stage. You can specify a target build stage. The
following command assumes you are using the previous `Dockerfile` but stops at
the stage named `builder`:

```bash
$ docker build --target builder -t alexellis2/href-counter:latest .
```

A few scenarios where this might be very powerful are:

- Debugging a specific build stage
- Using a `debug` stage with all debugging symbols or tools enabled, and a
  lean `production` stage
- Using a `testing` stage in which your app gets populated with test data, but
  building for production using a different stage which uses real data

## Use an external image as a "stage"

When using multi-stage builds, you are not limited to copying from stages you
created earlier in your Dockerfile. You can use the `COPY --from` instruction to
copy from a separate image, either using the local image name, a tag available
locally or on a Docker registry, or a tag ID. The Docker client pulls the image
if necessary and copies the artifact from there. The syntax is:

```dockerfile
COPY --from=nginx:latest /etc/nginx/nginx.conf /nginx.conf
```

## Use a previous stage as a new stage

You can pick up where a previous stage left off by referring to it when using the `FROM` directive. For example:

```dockerfile
FROM alpine:latest as builder
RUN apk --no-cache add build-base

FROM builder as build1
COPY source1.cpp source.cpp
RUN g++ -o /binary source.cpp

FROM builder as build2
COPY source2.cpp source.cpp
RUN g++ -o /binary source.cpp
```
