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Seeing problems with your applications? Take a look at your app logs and review these common issues and solutions.

Application restarts and crash messages

The platform automatically restarts application instances due to routine platform updates, which can be several times a week. If you review logs for an app that is functioning normally and you see recent messages about a series of instance restarts for no apparent reason, platform updates are probably the reason. This is normal and ok!

If you see recent messages such as The app crashed because of an unknown reason. and isn't handled, this may be because your application didn’t stop on request. The platform sends a request to apps to stop nicely so the platform can move them while this happens, but when they don’t stop on request, the platform force-kills them, reports them as crashed, and moves them anyway. Usually this doesn’t cause interruptions in service, just a few crash messages. To prevent the error messages, you can change your application to stop gracefully. In the recommended 12-factor app architecture, see the disposability factor.

If your application only has one instance, you may see brief interruptions in service during restarts due to routine platform updates. You can fix this by setting up multiple application instances.

Potential causes of issues during staging phase ([STG])

If you see problems in your logs in lines that include the label [STG], these explanations may help you resolve them.

App dependency specification

Dependencies are resolved during staging. For information beyond what’s presented in cf logs, use the the verbose logging option for your buildpack if available.

For example, cf set-env APPNAME VERBOSE true enables verbose logging for the default node.js buildpack.

App size and build complexity

  • Pushed application files must total less than 1GB. Use .cfignore to specify files which should be excluded from the push.
  • The combined size of application files and the specified buildpack must total less than 1.5GB.
  • The entire compiled droplet must total less than 4GB.
  • Staging must complete within 15 minutes and application must start within 5 minutes by default.

Buildpacks used

Cloud Foundry will attempt to detect the buildpack to use with your app by examining the application files. Use the buildpack: key in your manifest to specify a native buildpack by name or a custom buildpack by providing a URL. Override the buildpack setting and detection with the -b command line switch, which takes the same arguments.

Python dependency errors

If you’re seeing errors installing any Python dependencies, check whether you have a vendor/ directory in your app’s root. The Python buildpack won’t use PyPI if you have a vendor/ directory, so you’ll need to rename that directory to something else.

Potential causes of issues during app starting/stopping [CELL]

If you see problems in your logs in lines that include the label [CELL], these explanations may help you resolve them.

App manifest contents

When starting multiple apps via a single manifest tree, apps will start in the order they are encountered. Ensure worker apps running queues or migrations start before the apps which depend on them.

Command line options to cf push

By default, an application will start with a command specified by its buildpack. The command: in an application manifest will override the buildpack start command. The -c switch used with cf push overrides both the buildpack and manifest start commands.

Application start commands are cached during staging. Specifying a start command via -c does not update the staged command. Check the staged command with cf files APPNAME app_staging.yml. Specifying -c 'null' forces the buildpack start command to be used.

Environment variables and service bindings

  • Apps must listen on the port specified in the PORT environment variable.
  • Environment variables are updated when the app is staged and persist between application restarts. Be sure to run cf restage after updating variables.
  • Specify services in the application manifest via the application:key. Bindings will be created when the application is pushed. Avoid creating bindings after the fact with cf bind-service as that will create a hidden dependency.
  • Service instance credentials and connection parameters are stored in the JSON-formatted VCAP_SERVICES. The format of this variable differs between v1 and v2 services; see this section of the Cloud Foundry docs for more information.
  • Inspect the entire application environment including VCAP_SERVICES with cf env APPNAME.

Application start up time

By default, applications must start within 60 seconds. This timeout can be extended to a maximum of 180 second via the -t command line switch or timeout: manifest key.

Avoid placing long-running or multi-step tasks in the application start command. Consider using worker apps as part of a multi-application manifest instead.