As of February 2025, AWS App Runner supports Node.js 18 runtime. We can use it to run a Bun server.

• In AWS App Runner’s revised build process, building and running are done on separate containers. This means that commands installed by npm install -g during build time are not available during runtime.
• Bun binaries are also published to npm, so we can make use of that.

So deploying a Bun server to AWS App Runner consists of:

1. A Node.js project to install the Bun runtime. Its sole purpose is to have the Bun runtime binaries available during runtime.

   deployment/bun-runtime/package.json:

   {
     "dependencies": {
       "bun": "1.1.40"
     }
   }

2. An install script. It installs Bun and uses Bun to install the project dependencies:

   deployment/scripts/install.sh:

   #!/bin/bash -e
   bash -c 'cd deployment/bun-runtime && npm install'
   exec ./deployment/bun-runtime/node_modules/.bin/bun install

3. A start script. It configures the $PATH to include Bun binaries and starts the Bun server:

   deployment/scripts/start.sh:

   #!/bin/bash -e
   export PATH="$PWD/deployment/bun-runtime/node_modules/.bin:$PATH"
   exec bun start