web application update best practice..
normally how you folk do web application update from large critical system? do u forward user to page stating upgrading in progress on another web server; quickly deploy new war and point back ?
can provide some guides..
If possible, run two tomcat servers, with an Apache web server in front, load balancing the requests between the two.
When it comes time to upgrade, tell Apache to use only Tomcat A, then upgrade Tomcat B, tell Apache to use Tomcat B, upgrade Tomcat A, then back to using both.
No major interruption of service, if you do it right, although without session replication you're going to get some intra-session disruption. It's not as easy as it sounds, though.
As always, the lengths to which you go to minimise disruption depends on how important that disruption is. You can always make it smoother, at more expense and effort.
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We have a single Tomcat app server and a single front-end web server running Apache and mod_jk. Is it possible for us to add a second front-end web server, that points to the same app server and also runs Apache and mod_jk?
We don't want to do this for reasons of load balancing. Rather, it's for reasons of migration. The new web server will be an entirely different OS and will use a different SSO authentication module. We want to be able to stage and test it, switch a DNS entry to make it live, and decommission the old server.
The current workers.properties file looks like this:
worker.list=worker1
worker.worker1.type=ajp13
worker.worker1.host=10.x.x.x
worker.worker1.port=8009
Can I just duplicate that config onto a second web server?
I have no experience or background whatsoever with any of this, but have been asked to assist with a server migration and am trying my best to help.
I have been reading the documentation for mod_jk and Tomcat. I have found all sorts of documentation on pointing a single mod_jk instance to multiple Tomcat app servers, but nothing describing the opposite of that, which is what I'm trying to accomplish?
Is this possible?
Edit: I should note that we do not have any access to the Tomcat server, as it is managed by a third-party vendor. I'm sure they'd make changes if we asked them, but we don't have the ability to log into it ourselves.
Yes - duplicating will be easiest. Most important** is keeping the worker name the same.
One gotcha is making sure Tomcat has enough connections available to be handled by both web servers. The normal defaults are typically high enough, but if you try to stress test, the tomcat server may need the sum of workers available on the webservers. But if you don't have enough, Tomcat does write a warning to the logs.
** Most important - Ok - Not that important since you are not using sticky sessions. But could be confusing later if you try this experiment with 2 tomcats when switching between web servers.
Yes, of course you can. I have done it several times, even just to change the static files served by Apache (js, images, css) and test the Tomcat application with a different "skin".
Usually when building a high availability system, not only the Tomcat's or any other back-end servers get replicated, the front-end Apache or IIS or whatever is used gets replicated too.
As you said, it should be fine just copying the workers.properties file and the mapping rules in the Apache httpd's *.conf files.
An also, check with tomcat management team that the incoming connections to Tomcat's AJP port are not limited by net rules or firewalls, making just the old Apache able to reach the Tomcat.
Can I just duplicate that config onto a second web server?
Yes sure, since you want to hit the same Tomcat server so you can simply copy your worker.properties from Apache instance 1 to Apache instance 2. If you have only those 4 properties then nothing but if you have some properties like worker.worker1.cachesize=10 or worker.worker1.cache_timeout=600 and you want to play around then change it. But bottom line is that since you want to hit same Tomcat instance so you can simply copy.
Understanding it in non-tomcat way - you can have more than 1 HTTP web server like Apache intercepting all the requests and then forwarding it to same application or web server. However this is not common because common thing is a web server load balancing the requests for back end application servers.
I have been reading the documentation for mod_jk and Tomcat. I have
found all sorts of documentation on pointing a single mod_jk instance
to multiple Tomcat app servers, but nothing describing the opposite of
that, which is what I'm trying to accomplish?
Is this possible?
You couldn't find in any of the reading because what you are trying is a corner case, generally people configure multiple Tomcat workers to serve servlets on behalf of a certain web server in order to achieve load balancing, virtual hosting etc.
You mentioned that you are doing all this in order to test the Apache running on different OS and using different SSO, I am assuming there is no hardware load balancer sitting in front of your web servers (Apache) so how you are gonna hit your new Apache? I think you need to do this explicitly because your current URL will be pointing your first Apache, so in order to hit second/new Apache you need to give your testers/users the URL containing end point (IP:port) of second/new Apache. Even if you are doing all this locally still you need to have your second Apache listening on different port, or may be different IP but that's not common.
I have coded a Jersey based java server which is all wrapped in one excecutable jar.
I am looking for a web host service in which i can deploy the jar and run it.
I saw some dedicated servers which can do this but this is overshooting the need, any suggestions?
As per your comment I understand that you created a web application with a Jetty embedded server.
I think the best solution for you in this case is to get a virtual machine host, install JRE, upload your *.jar and run it from there. Given firewall permissions and correct configuration you should be able to receive requests on the 80 port. Cons? It costs. A lot.
Most of the Java hosts have already a servlet container running (almost always Tomcat) and you can only deploy your web application in it. Having an embedded Jetty server messes up everything for you.
I strongly suggest you to detach your web application (or as you called it REST server) from Jetty and deploy the *.war in any of the multiple free Java hosts to test it online.
EDIT
Thanks to you I made a deeper research on the topic and found an interesting guide to deploy a web application with embedded Jetty server in Heroku. I've never tried it nor I know if its free, but maybe you can give a try.
Digital Ocean work pretty well for me. Their basic packages are really cheap and you get root control over your own machine, meaning you can host whatever you want without restrictions. The only downside is that they are pretty old school - you have to set up EVERYTHING yourself, including firewalls etc. There are a lot of guides available on their website though, which makes life a lot easier!
http://www.digitalocean.com
I know this is a touch redundant but I don't have voting or comment rights yet so this is the only method for me to communicate.
Digital Ocean is a solid choice. I am paying 5$ a month for a VM with 512 Mb Ram and 20 gigs of storage (which for my use is just fine.) I am still working on my first proper deploy but as stated above there are tons of tutorials to guide you through it. I have no prior command line experience but I've managed to get the server running, Created an SSH key, uploaded my landing page and have gotten a test project using Spark as the embedded server up and functional in a matter of a few hours. The Droplets are easily scalable from what I've seen. I'm still having trouble deploying an Rest based app with Postgres as the DB but it seems more to do with the ports in play than anything else. Keep getting 404s.
I do understand that using the same tomcat instance for a number of web applications has some risks (e.g. if one web application crashes tomcat it will terminate the other web applications as well.). The benefit is of course cost effectiveness since one server is enough and having all the web applications in one place makes it very easy to administrate.
Are there any industry guidelines on how a good setup with multiple web applications on tomcat should look like?
Pros
One JVM to monitor
Common libraries can be shared (sometimes risky)
Cons
Common HTTP thread pool all applications are using (you can, however, configure several connectors with different thread pools)
One malfunctioning application can take down the whole server
Restarting one application requires restarting all of them (if not using hot-deployment)
You are right that hosting of multiple we applications on one application server / web container (either Tomcat or other) has benefits.
You mentioned the robustness issue when one application may cause failure of another. But let's simplify this: even if you have only one application you still want 24*7 availability. To achieve this goal people typically run more than one instance of application server with identical application on each one and load balancer in the enterence to the site. The same is relevant for several web applications. Just run N (2 as minimum) application servers with identical set of web applications deployed and load balancer. You will probably need a kind of watchdog that restarts server if it failed or if it stopped responding etc.
In some cases kind of clustering is required. But it is other story.
I am working at a startup, we are just about to roll out our first beta. Knowing that we will be having a good number of users, we want to have seamlessly deployment when we are adding new features.
I have worked with windows azure before, and I know they support seamless deployment, so I did some googling and cloudbees was the first result.
So the question is, with what we have now (geronimo server, rackspace hosting), is it possible to seamlessly redeploy a java web application? If so, how?
Are there other alternative solution, such as using another hosting provider or use a different web server? (Because it is a startup, it would be beneficial if the answer keeps scalability in mind)
If with a seamless redeploy, you mean an upgrade of your application without any downtime or restarting of your server, LiveRebel might be something to look at.
See http://zeroturnaround.com/liverebel
There are a lot of methods for doing this in the java world. If you don't use sessions (or use shared sessions between app servers) you can do a rolling stop/deploy/start of your appservers, taking 1 offline at a time and using a load balancer to ensure that traffic goes to the other servers.
I have heard Glassfish has such feature, the reference probably ment this (Glassfish 3.x redeploy command) : http://docs.oracle.com/cd/E19798-01/821-1758/6nmnj7q1h/index.html
So we have a busy legacy web service that needs to be replaced by a new one. The legacy web service was deployed using a WAR file on an apache tomcat server. That is it was copied over into the web apps folder under tomcat and all went well. I have been delegated with the task to replace it and would like to do it ensuring
I have a back up of the old service
the service gets replaced by another WAR file with no down time
Again I know I am being overly cautious however it is production level and I would like everything to go smooth. Step by step instructions would help.
Make a test server
Read tutorials and play around with the test server until it goes smoothly
Replicate what you did on the test server on the prod server.
If this really is a "busy prod server" with "no down time", then you will have some kind of test server that you can get the configuration right on.
... with no down time
If you literally mean zero downtime, then you will need to replicate your webserver and implement some kind of front-end that can transparently switch request streams to different servers. You will also need to deal with session migration.
If you mean with minimal downtime, then most web containers support hot redeployment of webapps. However, this typically entails an automatic shutdown and restart of the webapp, which may take seconds or minutes, depending on the webapp. Furthermore there is a risk of significant memory leakage; e.g. of permgen space.
The fallback is a complete shutdown / restart of the web container.
And it goes without saying that you need:
A test server that replicates your production environment.
A rigorous procedure for checking that deployments to your test environment result in a fully functioning system.
A preplanned, tested and hopefully bomb-proof procedure for rolling back your production system in the event of a failed deployment.
All of this (especially rollback) gets a lot more complicated when you system includes other stuff apart from the webapp; e.g. databases.