Use Compose Watch

Table of contents
Introduced in Docker Compose version 2.22.0

Use watch to automatically update and preview your running Compose services as you edit and save your code.

For many projects, this allows for a hands-off development workflow once Compose is running, as services automatically update themselves when you save your work.

watch adheres to the following file path rules:

  • All paths are relative to the project directory
  • Directories are watched recursively
  • Glob patterns aren't supported
  • Rules from .dockerignore apply
    • Use ignore option to define additional paths to be ignored (same syntax)
    • Temporary/backup files for common IDEs (Vim, Emacs, JetBrains, & more) are ignored automatically
    • .git directories are ignored automatically

You don't need to switch on watch for all services in a Compose project. In some instances, only part of the project, for example the Javascript frontend, might be suitable for automatic updates.

Compose Watch versus bind mounts

Compose supports sharing a host directory inside service containers. Watch mode does not replace this functionality but exists as a companion specifically suited to developing in containers.

More importantly, watch allows for greater granularity than is practical with a bind mount. Watch rules let you ignore specific files or entire directories within the watched tree.

For example, in a JavaScript project, ignoring the node_modules/ directory has two benefits:

  • Performance. File trees with many small files can cause high I/O load in some configurations
  • Multi-platform. Compiled artifacts cannot be shared if the host OS or architecture is different to the container

For example, in a Node.js project, it's not recommended to sync the node_modules/ directory. Even though JavaScript is interpreted, npm packages can contain native code that is not portable across platforms.

Configuration

The watch attribute defines a list of rules that control automatic service updates based on local file changes.

Each rule requires, a path pattern and action to take when a modification is detected. There are two possible actions for watch and depending on the action, additional fields might be accepted or required.

Watch mode can be used with many different languages and frameworks. The specific paths and rules will vary from project to project, but the concepts remain the same.

Prerequisites

In order to work properly, watch relies on common executables. Make sure your service image contains the following binaries:

  • stat
  • mkdir
  • rmdir
  • tar

watch also requires that the container's USER can write to the target path so it can update files. A common pattern is for initial content to be copied into the container using the COPY instruction in a Dockerfile. To ensure such files are owned by the configured user, use the COPY --chown flag:

# Run as a non-privileged user
FROM node:18-alpine
RUN useradd -ms /bin/sh -u 1001 app
USER app

# Install dependencies
WORKDIR /app
COPY package.json package.lock .
RUN npm install

# Copy source files into application directory
COPY --chown=app:app . /app

action

Sync

If action is set to sync, Compose makes sure any changes made to files on your host automatically match with the corresponding files within the service container.

sync is ideal for frameworks that support "Hot Reload" or equivalent functionality.

More generally, sync rules can be used in place of bind mounts for many development use cases.

Rebuild

If action is set to rebuild, Compose automatically builds a new image with BuildKit and replaces the running service container.

The behavior is the same as running docker compose up --build <svc>.

Rebuild is ideal for compiled languages or as fallbacks for modifications to particular files that require a full image rebuild (e.g. package.json).

Sync + Restart

If action is set to sync+restart, Compose synchronizes your changes with the service containers and restarts it.

sync+restart is ideal when config file changes, and you don't need to rebuild the image but just restart the main process of the service containers. It will work well when you update a database configuration or your nginx.conf file for example

Tip

Optimize your Dockerfile for speedy incremental rebuilds with image layer caching and multi-stage builds.

path and target

The target field controls how the path is mapped into the container.

For path: ./app/html and a change to ./app/html/index.html:

  • target: /app/html -> /app/html/index.html
  • target: /app/static -> /app/static/index.html
  • target: /assets -> /assets/index.html

Example

This minimal example targets a Node.js application with the following structure:

myproject/
├── web/
│   ├── App.jsx
│   └── index.js
├── Dockerfile
├── compose.yaml
└── package.json
services:
  web:
    build: .
    command: npm start
    develop:
      watch:
        - action: sync
          path: ./web
          target: /src/web
          ignore:
            - node_modules/
        - action: rebuild
          path: package.json

In this example, when running docker compose watch, a container for the web service is launched using an image built from the Dockerfile in the project's root. The web service runs npm start for its command, which then launches a development version of the application with Hot Module Reload enabled in the bundler (Webpack, Vite, Turbopack, etc).

After the service is up, the watch mode starts monitoring the target directories and files. Then, whenever a source file in the web/ directory is changed, Compose syncs the file to the corresponding location under /src/web inside the container. For example, ./web/App.jsx is copied to /src/web/App.jsx.

Once copied, the bundler updates the running application without a restart.

Unlike source code files, adding a new dependency can’t be done on-the-fly, so whenever package.json is changed, Compose rebuilds the image and recreates the web service container.

This pattern can be followed for many languages and frameworks, such as Python with Flask: Python source files can be synced while a change to requirements.txt should trigger a rebuild.

Use watch

  1. Add watch sections to one or more services in compose.yaml.
  2. Run docker compose watch to build and launch a Compose project and start the file watch mode.
  3. Edit service source files using your preferred IDE or editor.

Looking for a sample project to test things out?

Check out dockersamples/avatars, or local setup for Docker docs for a demonstration of Compose watch.

Feedback

We are actively looking for feedback on this feature. Give feedback or report any bugs you may find in the Compose Specification repository.

Reference