Default exposed ports of Azure App Service Linux Blessed Images

This post will quickly cover the default ports that are exposed on various Azure App Service Blessed Images

Overview

When deploying your application to Blessed Images - it should be known that these Docker images have already defined listening ports. Depending on the application, you’ll need to ensure you are not hardcoding a different port within code - as this port mismatch between what’s exposed on the running container and what your application is actually listening on will cause the container to time out on start up, due to this.

Ports

• Node:
  • Port 8080 is the default exposed port for the Node Blessed Image.
  • Unless you’re serving static content with the built-in PM2 installation, your Node server must be listening on this port - this can be listened on with the process.env.PORT which takes the current port value. Review the public documentation here on this - Get port number
• Python:
  • Port 8000 is the default exposed port for the Python Blessed Image.
  • Gunicorn is used as the default wSGI server to serve our Python entrypoint - Gunicorn also listens on 8000.
  • If you’re following how we detect Python applications here, then you should not need to worry about changing your port.
  • If you’re not following the default detection method, you should listen for the PORT environment variable, with something like os.environ.get('PORT', 8000)
• PHP:
  • Port 8080 is the default exposed port for the PHP Blessed Image. This uses NGINX by default as the Web Server which serves the deployed PHP files.
  • If you add the App Setting WEBSITES_DISABLE_FPM, this will pull a PHP Blessed Image using Apache - which also exposes port 8080 by default.
  • NGINX or Apache will be serving the PHP files.
• .NET:
  • Port 8080 is the default exposed port for the .NET Blessed Image. This expects a Web Server to be brought with your code (eg., Kestrel)
• Java SE:
  • Port 80 is the default exposed port for the Java SE Blessed Image. This expects an embedded Web Server like Tomcat, Jetty, Undertow, etc. to be packaged in the JAR being deployed - the port number is passed to the Web Server through the -Dserver.port setting, which is set as 80. This is default behavior for this image.
• Tomcat:
  • Port is 80 the default exposed port for the Tomcat Blessed Image. A WAR or JSP pages can be deployed here - which is what Tomcat will run.
• Go:
  • Port is 8080 the default exposed port for the Go Blessed Image (experimental). A Go HTTP Web Server is expected to be brought in the code being deployed. This can be listened on by the application in a ways uch as - err := http.ListenAndServe(":8080", nil)
• Ruby:
  • Port is 8080 the default exposed port for the Ruby Blessed Image.

How to change the exposed port

Adding the App Setting PORT to your new value will change the listening port. This will change the port exposed for the container in the docker run command.

Assuming the application is listening for the PORT environment variable (if applicable), this should be generally fine. If you’re hardcoding the value and make this change, your container will likely time out on startup due to the port value mismatch.

See this post - Whats the difference between PORT and WEBSITES_PORT - for more.