--- title: "Use bind mounts" keywords: > get started, setup, orientation, quickstart, intro, concepts, containers, docker desktop description: Using bind mounts in our application --- In [part 5](./05_persisting_data.md), you used a volume mount to persist the data in your database. A volume mount is a great choice when you need somewhere persistent to store your application data. A bind mount is another type of mount, which lets you share a directory from the host's filesystem into the container. When working on an application, you can use a bind mount to mount source code into the container. The container sees the changes you make to the code immediately, as soon as you save a file. This means that you can run processes in the container that watch for filesystem changes and respond to them. In this chapter, you'll see how you can use bind mounts and a tool called [nodemon](https://npmjs.com/package/nodemon){:target="_blank" rel="noopener" class="_"} to watch for file changes, and then restart the application automatically. There are equivalent tools in most other languages and frameworks. ## Quick volume type comparisons The following table outlines the main differences between volume mounts and bind mounts. | | Named volumes | Bind mounts | | -------------------------------------------- | -------------------------------------------------- | ---------------------------------------------------- | | Host location | Docker chooses | You decide | | Mount example (using `--mount`) | `type=volume,src=my-volume,target=/usr/local/data` | `type=bind,src=/path/to/data,target=/usr/local/data` | | Populates new volume with container contents | Yes | No | | Supports Volume Drivers | Yes | No | ## Trying out bind mounts Before looking at how you can use bind mounts for developing your application, you can run a quick experiment to get a practical understanding of how bind mounts work. 1. Open a terminal and change directory to the `app` directory of the getting started repository. 2. Run the following command to start `bash` in an `ubuntu` container with a bind mount.
```console $ docker run -it --mount type=bind,src="$(pwd)",target=/src ubuntu bash ```
Run this command in PowerShell. ```powershell $ docker run -it --mount "type=bind,src=$pwd,target=/src" ubuntu bash ```
The `--mount` option tells Docker to create a bind mount, where `src` is the current working directory on your host machine (`getting-started/app`), and `target` is where that directory should appear inside the container (`/src`). 3. After running the command, Docker starts an interactive `bash` session in the root directory of the container's filesystem. ```console root@ac1237fad8db:/# pwd / root@ac1237fad8db:/# ls bin dev home media opt root sbin srv tmp var boot etc lib mnt proc run src sys usr ``` 4. Change directory to the `src` directory. This is the directory that you mounted when starting the container. Listing the contents of this directory displays the same files as in the `getting-started/app` directory on your host machine. ```console root@ac1237fad8db:/# cd src root@ac1237fad8db:/src# ls Dockerfile node_modules package.json spec src yarn.lock ``` 5. Create a new file named `myfile.txt`. ```console root@ac1237fad8db:/src# touch myfile.txt root@ac1237fad8db:/src# ls Dockerfile myfile.txt node_modules package.json spec src yarn.lock ``` 6. Open the `app` directory on the host and observe that the `myfile.txt` file is in the directory. ``` ├── app/ │ ├── Dockerfile │ ├── myfile.txt │ ├── node_modules/ │ ├── pacakge.json │ ├── spec/ │ ├── src/ │ └── yarn.lock ``` 7. From the host, delete the `myfile.txt` file. 8. In the container, list the contents of the `app` directory once more. Observe that the file is now gone. ```console root@ac1237fad8db:/src# ls Dockerfile node_modules package.json spec src yarn.lock ``` 9. Stop the interactive container session with `Ctrl` + `D`. That's all for a brief introduction to bind mounts. This procedure demonstrated how files are shared between the host and the container, and how changes are immediately reflected on both sides. Now you can use bind mounts to develop software. ## Development containers Using bind mounts is common for local development setups. The advantage is that the development machine doesn’t need to have all of the build tools and environments installed. With a single docker run command, Docker pulls dependencies and tools. ### Run your app in a development container The following steps describe how to run a development container with a bind mount that does the following: - Mount your source code into the container - Install all dependencies - Start `nodemon` to watch for filesystem changes You can use the CLI or Docker Desktop to run your container with a bind mount.
1. Make sure you don't have any `getting-started` containers currently running. 2. Run the following command from the `getting-started/app` directory.
```console $ docker run -dp 127.0.0.1:3000:3000 \ -w /app --mount type=bind,src="$(pwd)",target=/app \ node:18-alpine \ sh -c "yarn install && yarn run dev" ``` The following is a breakdown of the command: - `-dp 127.0.0.1:3000:3000` - same as before. Run in detached (background) mode and create a port mapping - `-w /app` - sets the "working directory" or the current directory that the command will run from - `--mount type=bind,src="$(pwd)",target=/app` - bind mount the current directory from the host into the `/app` directory in the container - `node:18-alpine` - the image to use. Note that this is the base image for your app from the Dockerfile - `sh -c "yarn install && yarn run dev"` - the command. You're starting a shell using `sh` (alpine doesn't have `bash`) and running `yarn install` to install packages and then running `yarn run dev` to start the development server. If you look in the `package.json`, you'll see that the `dev` script starts `nodemon`.
Run this command in PowerShell. ```powershell $ docker run -dp 127.0.0.1:3000:3000 ` -w /app --mount "type=bind,src=$pwd,target=/app" ` node:18-alpine ` sh -c "yarn install && yarn run dev" ``` The following is a breakdown of the command: - `-dp 127.0.0.1:3000:3000` - same as before. Run in detached (background) mode and create a port mapping - `-w /app` - sets the "working directory" or the current directory that the command will run from - `--mount "type=bind,src=$pwd,target=/app"` - bind mount the current directory from the host into the `/app` directory in the container - `node:18-alpine` - the image to use. Note that this is the base image for your app from the Dockerfile - `sh -c "yarn install && yarn run dev"` - the command. You're starting a shell using `sh` (alpine doesn't have `bash`) and running `yarn install` to install packages and then running `yarn run dev` to start the development server. If you look in the `package.json`, you'll see that the `dev` script starts `nodemon`.
3. You can watch the logs using `docker logs `. You'll know you're ready to go when you see this: ```console $ docker logs -f nodemon src/index.js [nodemon] 2.0.20 [nodemon] to restart at any time, enter `rs` [nodemon] watching dir(s): *.* [nodemon] starting `node src/index.js` Using sqlite database at /etc/todos/todo.db Listening on port 3000 ``` When you're done watching the logs, exit out by hitting `Ctrl`+`C`.
1. Make sure you don't have any `getting-started` containers currently running. 2. Run the image with a bind mount. 1. Select the search box at the top of Docker Desktop. 2. In the search window, select the **Images** tab. 3. In the search box, specify the container name, `getting-started`. > **Tip** > > Use the search filter to filter images and only show **Local images**. 4. Select your image and then select **Run**. 5. Select **Optional settings**. 6. In **Host path**, specify the path to the `app` directory on your host machine. 7. In **Container path**, specify `/app`. 8. Select **Run**. 3. You can watch the container logs using Docker Desktop 1. Select **Containers** in Docker Desktop. 2. Select your container name. You'll know you're ready to go when you see this: ```console $ docker logs -f nodemon src/index.js [nodemon] 2.0.20 [nodemon] to restart at any time, enter `rs` [nodemon] watching dir(s): *.* [nodemon] starting `node src/index.js` Using sqlite database at /etc/todos/todo.db Listening on port 3000 ```
### Develop your app with the development container Update your app on your host machine and see the changes reflected in the container. 1. In the `src/static/js/app.js` file, on line 109, change the "Add Item" button to simply say "Add": ```diff - {submitting ? 'Adding...' : 'Add Item'} + {submitting ? 'Adding...' : 'Add'} ``` Save the file. 2. Refresh the page in your web browser, and you should see the change reflected almost immediately. It might take a few seconds for the Node server to restart. If you get an error, try refreshing after a few seconds. ![Screenshot of updated label for Add button](images/updated-add-button.png){: style="width:75%;" .text-center} 3. Feel free to make any other changes you'd like to make. Each time you make a change and save a file, the `nodemon` process restarts the app inside the container automatically. When you're done, stop the container and build your new image using: ```console $ docker build -t getting-started . ``` ## Next steps At this point, you can persist your database and see changes in your app as you develop without rebuilding the image. In addition to volume mounts and bind mounts, Docker also supports other mount types and storage drivers for handling more complex and specialized use cases. To learn more about the advanced storage concepts, see [Manage data in Docker](https://docs.docker.com/storage/). In order to prepare your app for production, you need to migrate your database from working in SQLite to something that can scale a little better. For simplicity, you'll keep using a relational database and switch your application to use MySQL. But, how should you run MySQL? How do you allow the containers to talk to each other? You'll learn about that in the next section. [Multi container apps](07_multi_container.md){: .button .primary-btn}