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How to advice deploying war files vs executable jar with embedded container

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In this tutorial we are going to learn about deploying war files vs executable jar with embedded container.

An interesting question. This is just my view on the topic, so take everything with a grain of salt. I have occasionally deployed and managed applications using both servlet containers and embedded servers. I’m sure there are still many good reasons for using servlet containers but I will try to just focus on why they are less popular today.

Short version: Servlet containers are great to manage multiple applications on a single host but don’t seem very useful to manage just one single application. With cloud environments, a single application per virtual machine seems preferable and more common. Modern frameworks want to be cloud compatible, therefore the shift to embedded servers.

So I think cloud services are the main reason for abandoning servlet containers. Just like servlet containers let you manage applications, cloud services let you manage virtual machines, instances, data storage and much more. This sounds more complicated, but with cloud environments, there has been a shift to single app machines.

This means you can often treat the whole machine like it is the application. Each application runs on a machine with appropriate size. Cloud instances can pop up and vanish at any time which is great for scaling. If an application needs more resources, you create more instances.

Dedicated servers on the other hand usually are powerful but with a fixed size, so you run multiple applications on a single machine to maximize the use of resources. Managing dozens of application - each with their own configurations, web servers, routes and connections etc. - is not fun, so using a servlet container helps you to keep everything manageable and yourself sane. It is harder to scale though. Servlet containers in the cloud don’t seem very useful. They would have to be set up for each tiny instance, without providing much value since they only manage a single application.

Also, clouds are cool and non-cloud stuff is boring (if we still believe the hype). Many frameworks try to be scalable by default, so that they can easily be deployed to the clouds. Embedded servers are fast to deploy and run so they seem like a reasonable solution. Servlet containers are usually still supported but require a more complicated set up.

Some other points:

  • The embedded server could be optimized for the framework or is better integrated with the frameworks tooling (like the play console for example).
  • Not all cloud environments come with customizable machine images. Instead of writing initialization scripts to download and set up servlet containers, using dedicated software for cloud application deployments is much simpler.
  • I have yet to find a Tomcat setup that doesn’t greet you with a perm gen space error every few redeployments of your app. Taking a bit longer to (re-)start embedded servers is no problem when you can almost instantly switch between staging and production instances without any downtime.
  • As already mentioned in the question, it’s very convenient for the end user to just run the application.
  • Embedded servers are portable and convenient for development. Today everything is rapid, prototypes and MVPs need to be created and delivered as fast as possible. No one wants to spend too much time setting up an environment for every developer.