---
title: Using Bake with additional contexts
linkTitle: Contexts
weight: 80
description: |
  Additional contexts are useful when you want to pin image versions,
  or reference the output of other targets
keywords: build, buildx, bake, buildkit, hcl
aliases:
  - /build/customize/bake/build-contexts/
  - /build/bake/build-contexts/
---

In addition to the main `context` key that defines the build context, each
target can also define additional named contexts with a map defined with key
`contexts`. These values map to the `--build-context` flag in the [build
command](/reference/cli/docker/buildx/build.md#build-context).

Inside the Dockerfile these contexts can be used with the `FROM` instruction or
`--from` flag.

Supported context values are:

- Local filesystem directories
- Container images
- Git URLs
- HTTP URLs
- Name of another target in the Bake file

## Pinning alpine image

```dockerfile {title=Dockerfile}
# syntax=docker/dockerfile:1
FROM alpine
RUN echo "Hello world"
```

```hcl {title=docker-bake.hcl}
target "app" {
  contexts = {
    alpine = "docker-image://alpine:3.13"
  }
}
```

## Using a secondary source directory

```dockerfile {title=Dockerfile}
FROM golang
COPY --from=src . .
```

```hcl {title=docker-bake.hcl}
# Running `docker buildx bake app` will result in `src` not pointing
# to some previous build stage but to the client filesystem, not part of the context.
target "app" {
  contexts = {
    src = "../path/to/source"
  }
}
```

## Using a target as a build context

To use a result of one target as a build context of another, specify the target
name with `target:` prefix.

```dockerfile {title=baseapp.Dockerfile}
FROM scratch
```
```dockerfile {title=Dockerfile}
# syntax=docker/dockerfile:1
FROM baseapp
RUN echo "Hello world"
```

```hcl {title=docker-bake.hcl}
target "base" {
  dockerfile = "baseapp.Dockerfile"
}

target "app" {
  contexts = {
    baseapp = "target:base"
  }
}
```

In most cases you should just use a single multi-stage Dockerfile with multiple
targets for similar behavior. This case is only recommended when you have
multiple Dockerfiles that can't be easily merged into one.

## Deduplicate context transfer

> [!NOTE]
>
> As of Buildx version 0.17.0 and later, Bake automatically de-duplicates
> context transfer for targets that share the same context. In addition to
> Buildx version 0.17.0, the builder must be running BuildKit version 0.16.0 or
> later, and the Dockerfile syntax must be `docker/dockerfile:1.10` or later.
>
> If you meet these requirements, you don't need to manually de-duplicate
> context transfer as described in this section.
>
> - To check your Buildx version, run `docker buildx version`.