Configure Your Backend Application

Configure a Backend Capsule in the Config tab.

Set Capsule Parameters

The Capsule Parameters section is split into Build and Runtime, each with its own Edit link:

Section	Settings	When you save
Build	Project Path, Run Command	Rebuilds and deploys the capsule
Runtime	Network Port, Health Check	Redeploys the capsule, without a new build

To change a setting:

1. Click Edit next to Build or Runtime.
2. Update the settings.
3. Click Save, then confirm.

You can edit one section at a time.

Build settings

Changing build settings starts a new build

When you save a change in Build, Code Capsules rebuilds your code with the new settings and deploys the result. A build can take a few minutes.

Project Path

The Project Path specifies the path to your code. The default is /, which works for most projects.

Run Command

Use the Run Command field to specify how to start your app. Leave this field empty to use the default command for the Capsule type, or enter a custom command:

• Python: python app.py
• Node.js: npm start
• Ruby: ruby app.rb

Runtime settings

Changing runtime settings redeploys the capsule

When you save a change in Runtime, Code Capsules redeploys the capsule with the new settings, replacing its running replicas. It does not start a new build.

Network Port

The Network Port is the port your app runs on. Your app must be configured to listen on this port. The default is 3000.

Health Check

A health check tells Code Capsules when your app is ready for traffic, and restarts replicas that stop responding. To set one:

1. In the Capsule Parameters section, click Edit next to Runtime.
2. Set Health Check to Automatic or Manual.
3. Enter the Endpoint your app responds to, for example /health. With Manual, also set Timeout (seconds) and Time to First Check (seconds).
4. Click Save, then confirm.

See Health checks for each setting, how failing replicas are handled, and how to write a good endpoint.

Set Environment Variables

Each Backend Capsule is automatically assigned an APP_URL environment variable that stores its public URL.

To view environment variable values, click show in the top-right corner of the table.

To add or edit custom variables:

1. Click Key/Val Editor or Text Editor in the top-right corner.
2. Enter or update the variable’s Name and Value.
3. Click Save to apply your changes.

Connect Data Capsules

Connect a Database Capsule

In the Data capsules section, click the View button next to a Database Capsule to see its connection details.

Click + next to the Connection string variable to create a DATABASE_URL environment variable in your Backend Capsule. Your application will use this variable to connect to and use the services provided by the Database Capsule.

Connect a Persistent Storage Capsule

Click Bind next to the Persistent Storage Capsule to attach it to your Backend Capsule.

During the bind process, Code Capsules creates a PERSISTENT_STORAGE_DIR environment variable that tells your Backend Capsule where to access the Persistent Storage Capsule.