This is a quick post exploring the usefulness of AWS Elastic Beanstalk Environment Configuration files using “.ebextensions”.
.ebextensions config files, written in YAML (http://yaml.org/), can be used to set up the server platform by automatically performing various custom actions and configuration when an application is uploaded to AWS Elastic Beanstalk.
Through .ebextensions you can:
- Create configuration or other files (SSL certificates, etc) on the server machine
- Install packages/programs
- Start/stop services
- Execute custom commands
- And much more
This can help you set up a new or existing server, as far as the configuration on the server machine is concerned, without manually having to do it yourself every time you deploy a new application.
Since I’m most familiar with how .ebextensions work using Java .war’s deployed to AWS Elastic Beanstalk, here’s a quick rundown on how to set it up for your Java environment: in your web project’s WebContent folder, create a folder called “.ebextensions”. Then within the .ebextensions folder you can create one or many files ending with a .config extension. Any and all .config files within the .ebextensions (ProjectRoot/WebContent/.ebextensions/*.config) will get executed after you upload the .war file for your project to AWS Elastic Beanstalk.
So if you’re using AWS Elastic Beanstalk and aren’t yet using .ebextensions, I would highly recommend you look into it. There is more documentation here: http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/ebextensions.html
This took me a long time to figure out, so I thought I’d share it with anyone else struggling with this.
When you upload a Vaadin application to the AWS Elastic Beanstalk, Tomcat sits behind an Apache server that proxies connections to it. (Note: this may apply to you even if you’re not in AWS/ElasticBeanstalk. If you use Apache as a proxy to an application server, be it Tomcat or something else, this could still be an issue).
If you’re using Vaadin push in long polling mode (Transport.LONG_POLLING), it turns out that the connection between the client (browser) and server (tomcat, or your other java application server) gets dropped due to a timeout issue. If there is no data exchanged between the server (tomcat) and the client (browser), then the connection is deemed “idle” by Apache and gets dropped. This is an issue because with long polling, the HTTP connection remains open indefinitely, and that’s information is pushed to the client from the server.
Now with Vaadin’s push, it’s supposed to recover from a dropped connection. The connection is supposed to just get reestablished, and everything resumes. That’s an ideal scenario. In my experience, that doesn’t always work the way it should. If I’m on a Vaadin web app through my browser, and sit idle for a while, when I come back to it a lot of time it resumes fine (I can see push reestablishing itself in the console), but a lot of times the app just hangs forever.
Another thing to note is that Vaadin sends a heartbeat to the client, to check if the client is still there. The default heartbeat is every 5 minutes. When a heartbeat is sent, Apache’s idle connection timeout is reset. So if there is no user activity for a few minutes, the goal is to adjust the configuration so that the heartbeat happens before Apache times out the HTTP connection.
So the solution for this is to
- Modify Apache’s timeout for idle connections. I believe the default setting in AWS’s configuration for Apache, is 60 seconds. You’ll need to ssh into your server, edit /etc/httpd/conf/httpd.conf, and look for the “Timeout” directive. Change the Timeout directive to be greater-than the default Vaadin heartbeat of 5 minutes. Try 6 minutes (note: the Timeout value is in seconds), so you’d set “Timeout 360”. The downside of this approach is if your server has hundreds of thousands of requests, surely some legitimately idle connections (where the client is gone without cleaning up and not coming back) will linger for longer than 60 seconds, this affecting your system performance.
- Modify Vaadin’s heartbeat to be less than 60 seconds. You can edit your web.xml, and add an heartbeatInterval parameter like so:
- You can tweak both the Vaadin heartbeat, and the Apache Timeout value to some reasonable values that suit your needs the best. Just make sure that the heartbeat interval is shorter than the timeout.