import Callout from "../../../../components/Callout";

# Deploying with Docker

Building a [Docker](https://www.docker.com/) image is a common way to deploy all sorts of applications. However, doing so from a monorepo has several challenges.

## The problem

**TL;DR:** In a monorepo, unrelated changes can make Docker do unnecessary work when deploying your app.

Let's imagine you have a monorepo that looks like this:

```txt
├── apps
│   ├── docs
│   │   ├── server.js
│   │   └── package.json
│   └── web
│       └── package.json
├── package.json
└── package-lock.json
```

You want to deploy `apps/docs` using Docker, so you create a Dockerfile:

```docker filename="Dockerfile"
FROM node:16

WORKDIR /usr/src/app

# Copy root package.json and lockfile
COPY package.json ./
COPY package-lock.json ./

# Copy the docs package.json
COPY apps/docs/package.json ./apps/docs/package.json

RUN npm install

# Copy app source
COPY . .

EXPOSE 8080

CMD [ "node", "apps/docs/server.js" ]
```

This will copy the root `package.json` and the root lockfile to the docker image. Then, it'll install dependencies, copy the app source and start the app.

You should also create a `.dockerignore` file to prevent node_modules from being copied in with the app's source.

```txt filename=".dockerignore"
node_modules
npm-debug.log
```

### The lockfile changes too often

Docker is pretty smart about how it deploys your apps. Just like Turbo, it tries to do as [little work as possible](https://bitjudo.com/blog/2014/03/13/building-efficient-dockerfiles-node-dot-js/).

In our Dockerfile's case, it will only run `npm install` if the files it has in its image are _different_ from the previous run. If not, it'll restore the `node_modules` directory it had before.

This means that whenever `package.json`, `apps/docs/package.json` or `package-lock.json` change, the docker image will run `npm install`.

This sounds great - until we realise something. The `package-lock.json` is _global_ for the monorepo. That means that **if we install a new package inside `apps/web`, we'll cause `apps/docs` to redeploy**.

In a large monorepo, this can result in a huge amount of lost time, as any change to a monorepo's lockfile cascades into tens or hundreds of deploys.

## The solution

The solution is to prune the inputs to the Dockerfile to only what is strictly necessary. Turborepo provides a simple solution - `turbo prune`.

```bash
turbo prune --scope="docs" --docker
```

Running this command creates a **pruned version of your monorepo** inside an `./out` directory. It only includes workspaces which `docs` depends on.

Crucially, it also **prunes the lockfile** so that only the relevant `node_modules` will be downloaded.

### The `--docker` flag

By default, `turbo prune` puts all relevant files inside `./out`. But to optimize caching with Docker, we ideally want to copy the files over in two stages.

First, we want to copy over only what we need to install the packages. When running `--docker`, you'll find this inside `./out/json`.

```txt
out
├── json
│   └── apps
│       └── docs
│           └── package.json
├── full
│   └── apps
│       └── docs
│           ├── server.js
│           └── package.json
└── package-lock.json
```

Afterwards, you can copy the files in `./out/full` to add the source files.

Splitting up **dependencies** and **source files** in this way lets us **only run `npm install` when dependencies change** - giving us a much larger speedup.

<Callout type="info">
  Without `--docker`, all pruned files are placed inside `./out`.
</Callout>

### Example

Our detailed [`with-docker` example](https://github.com/vercel/turbo/tree/main/examples/with-docker) goes into depth on how to utilise `prune` to its full potential. Here's the Dockerfile, copied over for convenience.

```docker
FROM node:alpine AS builder
RUN apk add --no-cache libc6-compat
RUN apk update
# Set working directory
WORKDIR /app
RUN yarn global add turbo
COPY . .
RUN turbo prune --scope=web --docker

# Add lockfile and package.json's of isolated subworkspace
FROM node:alpine AS installer
RUN apk add --no-cache libc6-compat
RUN apk update
WORKDIR /app

# First install the dependencies (as they change less often)
COPY .gitignore .gitignore
COPY --from=builder /app/out/json/ .
COPY --from=builder /app/out/yarn.lock ./yarn.lock
RUN yarn install

# Build the project
COPY --from=builder /app/out/full/ .
COPY turbo.json turbo.json
RUN yarn turbo run build --filter=web...

FROM node:alpine AS runner
WORKDIR /app

# Don't run production as root
RUN addgroup --system --gid 1001 nodejs
RUN adduser --system --uid 1001 nextjs
USER nextjs

COPY --from=installer /app/apps/web/next.config.js .
COPY --from=installer /app/apps/web/package.json .

# Automatically leverage output traces to reduce image size
# https://nextjs.org/docs/advanced-features/output-file-tracing
COPY --from=installer --chown=nextjs:nodejs /app/apps/web/.next/standalone ./
COPY --from=installer --chown=nextjs:nodejs /app/apps/web/.next/static ./apps/web/.next/static

CMD node apps/web/server.js
```

## Remote caching

To take advantage of remote caches during Docker builds, you will need to make sure your build container has credentials to access your Remote Cache.

There are many ways to take care of secrets in a Docker image. We will use a simple strategy here with multi-stage builds using secrets as build arguments that will get hidden for the final image.

Assuming you are using a Dockerfile similar to the one above, we will bring in some environment variables from build arguments right before `turbo build`:

```docker
ARG TURBO_TEAM
ENV TURBO_TEAM=$TURBO_TEAM

ARG TURBO_TOKEN
ENV TURBO_TOKEN=$TURBO_TOKEN

RUN yarn turbo run build --filter=web...
```

`turbo` will now be able to hit your remote cache. To see a Turborepo cache hit for a non-cached Docker build image, run a command like this one from your project root:

```sh
docker build -f apps/web/Dockerfile . --build-arg TURBO_TEAM=“your-team-name” --build-arg TURBO_TOKEN=“your-token“ --no-cache
```
