# Editing the build specification You can customize an application's build settings by editing the build specification (buildspec) in the Amplify console. The build settings are applied to all the branches in your app, except for the branches that have an `amplify.yml` file saved in the Git repository. **To edit build settings in the Amplify console** 1. Sign in to the AWS Management Console and open the [Amplify console](https://console.aws.amazon.com/amplify/). 1. Choose the app that you want to edit the build settings for. 1. In the navigation pane, choose **Hosting**, then choose **Build settings**. 1. On the **Build settings** page, in the **App build specification** section, choose **Edit**. 1. In the **Edit build spec** window, enter your updates. 1. Choose **Save**. You can use the examples described in the following topics to update your build settings for specific scenarios. **Topics** + [Setting branch-specific build settings with scripting](#branch-specific-build-settings) + [Setting a command to navigate to a subfolder](#navigating-to-a-subfolder) + [Deploying the backend with the front end for a Gen 1 app](#frontend-with-backend) + [Setting the output folder](#setting-the-output-folder) + [Installing packages as part of a build](#installing-packages-as-part-of-your-build) + [Using a private npm registry](#using-a-private-npm-registry) + [Installing OS packages](#installing-os-packages) + [Setting key-value storage for every build](#key-value-storage-for-every-build) + [Skipping the build for a commit](#skip-build-for-a-commit) + [Turning off automatic builds on every commit](#disable-automatic-builds) + [Configuring diff based frontend build and deploy](#enable-diff-deploy) + [Configuring diff based backend builds for a Gen 1 app](#enable-diff-backend) ## Setting branch-specific build settings with scripting You can use bash shell scripting to set branch-specific build settings. For example, the following script uses the system environment variable *\$1AWS\$1BRANCH* to run one set of commands if the branch name is *main* and a different set of commands if the branch name is *dev*. ``` frontend: phases: build: commands: - if [ "${AWS_BRANCH}" = "main" ]; then echo "main branch"; fi - if [ "${AWS_BRANCH}" = "dev" ]; then echo "dev branch"; fi ``` ## Setting a command to navigate to a subfolder For monorepos, users want to be able to `cd` into a folder to run the build. After you run the `cd` command, it applies to all stages of your build so you don’t need to repeat the command in separate phases. ``` version: 1 env: variables: key: value frontend: phases: preBuild: commands: - cd react-app - npm ci build: commands: - npm run build ``` ## Deploying the backend with the front end for a Gen 1 app **Note** This section applies to Amplify Gen 1 applications only. A Gen 1 backend is created using Amplify Studio and the Amplify command line interface (CLI). The `amplifyPush` command is a helper script that helps you with backend deployments. The build settings below automatically determine the correct backend environment to deploy for the current branch. ``` version: 1 env: variables: key: value backend: phases: build: commands: - amplifyPush --simple ``` ## Setting the output folder The following build settings set the output directory to the public folder. ``` frontend: phases: commands: build: - yarn run build artifacts: baseDirectory: public ``` ## Installing packages as part of a build You can use the `npm` or `yarn` commands to install packages during the build. ``` frontend: phases: build: commands: - npm install -g - deploy - yarn run build artifacts: baseDirectory: public ``` ## Using a private npm registry You can add references to a private registry in your build settings or add it as an environment variable. ``` build: phases: preBuild: commands: - npm config set - npm config set registry https://registry.npmjs.org - npm config set always-auth true - npm config set email hello@amplifyapp.com - yarn install ``` ## Installing OS packages Amplify's AL2023 image runs your code with a non-privileged user named `amplify`. Amplify grants this user privileges to run OS commands using the Linux `sudo` command. If you want to install OS packages for missing dependencies, you can use commands such as `yum` and `rpm` with `sudo`. The following example build section demonstrates the syntax for installing an OS package using the `sudo` command. ``` build: phases: preBuild: commands: - sudo yum install -y ``` ## Setting key-value storage for every build The `envCache` provides key-value storage at build time. Values stored in the `envCache` can only be modified during a build and can be re-used at the next build. Using the `envCache`, we can store information on the deployed environment and make it available to the build container in successive builds. Unlike values stored in the `envCache`, changes to environment variables during a build are not persisted to future builds. Example usage: ``` envCache --set envCache --get ``` ## Skipping the build for a commit To skip an automatic build on a particular commit, include the text **[skip-cd]** at the end of the commit message. ## Turning off automatic builds on every commit You can configure Amplify to turn off automatic builds on every code commit. To set up, choose **App settings**, **Branch settings**, and then locate the **Branches** section that lists the connected branches. Select a branch, and then choose **Actions**, **Disable auto build**. New commits to that branch will no longer start a new build. ## Configuring diff based frontend build and deploy You can configure Amplify to use diff based frontend builds. If enabled, at the start of each build Amplify attempts to run a diff on either your `appRoot`, or the `/src/` folder by default. If Amplify doesn't find any differences, it skips the frontend build, test (if configured), and deploy steps, and does not update your hosted app. **To configure diff based frontend build and deploy** 1. Sign in to the AWS Management Console and open the [Amplify console](https://console.aws.amazon.com/amplify/). 1. Choose the app to configure diff based frontend build and deploy for. 1. In the navigation pane, choose **Hosting**, **Environment variables**. 1. In the **Environment variables** section, choose **Manage variables**. 1. The procedure for configuring the environment variable varies depending on whether you are enabling or disabling diff based frontend build and deploy. + To enable diff based frontend build and deploy 1. In the **Manage variables** section, under **Variable**, enter `AMPLIFY_DIFF_DEPLOY`. 1. For **Value**, enter `true`. + To disable diff based frontend build and deploy 1. Do one of the following: + In the **Manage variables** section, locate `AMPLIFY_DIFF_DEPLOY`. For **Value**, enter `false`. + Remove the `AMPLIFY_DIFF_DEPLOY` environment variable. 1. Choose **Save**. Optionally, you can set the `AMPLIFY_DIFF_DEPLOY_ROOT` environment variable to override the default path with a path relative to the root of your repo, such as `dist`. ## Configuring diff based backend builds for a Gen 1 app **Note** This section applies to Amplify Gen 1 applications only. A Gen 1 backend is created using Amplify Studio and the Amplify command line interface (CLI). You can configure Amplify Hosting to use diff based backend builds using the `AMPLIFY_DIFF_BACKEND` environment variable. When you enable diff based backend builds, at the start of each build Amplify attempts to run a diff on the `amplify` folder in your repository. If Amplify doesn't find any differences, it skips the backend build step, and doesn't update your backend resources. If your project doesn't have an `amplify` folder in your repository, Amplify ignores the value of the `AMPLIFY_DIFF_BACKEND` environment variable. If you currently have custom commands specified in the build settings of your backend phase, conditional backend builds won't work. If you want those custom commands to run, you must move them to the frontend phase of your build settings in your app's `amplify.yml` file. **To configure diff based backend builds** 1. Sign in to the AWS Management Console and open the [Amplify console](https://console.aws.amazon.com/amplify/). 1. Choose the app to configure diff based backend builds for. 1. In the navigation pane, choose **Hosting**, **Environment variables**. 1. In the **Environment variables** section, choose **Manage variables**. 1. The procedure for configuring the environment variable varies depending on whether you are enabling or disabling diff based backend builds. + To enable diff based backend builds 1. In the **Manage variables** section, under **Variable**, enter `AMPLIFY_DIFF_BACKEND`. 1. For **Value**, enter `true`. + To disable diff based backend builds 1. Do one of the following: + In the **Manage variables** section, locate `AMPLIFY_DIFF_BACKEND`. For **Value**, enter `false`. + Remove the `AMPLIFY_DIFF_BACKEND` environment variable. 1. Choose **Save**.