Hey Baldur, On Mon, Apr 28, 2014 at 8:00 AM, Baldur <baldur....@gmail.com> wrote:
> Hi all, > > I'd like to get some help about my current architecture. > The > current scenario uses mod_jk to connect Apache httpd and Tomcat6. I have > two > Tomcat instances (using DeltaManager for session replication and sticky > session enabled) in order to provide high availability and balance load > across instances. Currently Tomcat manages 28 webapps and 7 of them are > only web services. Generally speaking, a webapp usually involves JSF or > Struts while a web services war involves JAX-WS. Both types of application > have a common stack implemented with Spring and Hibernate. As a result, > each > application produces a war of around 40-50 MB. > > Here are some questions that can make us better understand your environment and further the discussion on your choices: 1. What kind of hardware do you run these two instances on (single box, 2 boxes, how much RAM, etc..)? Do you have resources to run more Tomcat instances on this(these) box(es)? 2. Do you have HA as requirement for all the apps? Do you have any specific SLAs (service level agreements) you need to maintain? 3. Can you live without session replication, and just live with the sticky sessions? What kind of data do you keep in your sessions? How big are these sessions? 4. What's the order of magnitude for your concurrent users (100s, 1000s, 10000s) for these applications? I.e how many concurrent sessions do you need to maintain? 5. Are your webservices stateless, most of them usually are? 6. Do these applications share any libraries (Hibernate, Struts2, Spring, etc...)? What is the upgrade/release cycle for these applications? How do you deal with differences in versioning, e.g. Hibernate3 vs Hibernate4, or Spring 3.0 vs Spring 3.2 vs Spring 4.0, etc... In the ideal world, with infinite amount of resources (hardware, staff, etc) - I would have one Tomcat instance (or one cluster) per application, so I can segregate and isolate my application environments (JVMs). However, given huge number of applications, and that we don't have that much money to spare - that segregation might be too extreme, too wasteful - so we typically organize our applications to co-exist on the Tomcat instance(s), based on their importance, SLA agreements, release lifecycle, business operations, etc. > I'd like to ask you several questions to provide better > performance: > > * Which approach would be appropriate for this scenario? All wars > in > one cluster? Maybe move web services to other cluster? > > It might be useful to move webservices to a separate cluster that might not need session replication. You might gain some performance benefit by not having to replicate sessions across cluster members. Though, having 28 webapps (wars) on the same instance (clustered instance), my concern is isolation. What happens if one application trashes one of your JVMs? Then all other 27 apps are going to suffer and stress your other JVM. If you truly need HA, consider moving these apps on their own environment, independent of other apps. > * In order to improve deployments, which technique can I use to > minimize war size? Will be the cause of memory issues? I have tried to put > some common jars (spring, apache-commons and so on) in Tomcat lib but I > don't know if there is a better approach by other means. > > Have you observed any issues with the sizing of the apps, e.g. OutOfMemoryError (permgen space)? Ultimately, if you deploy ton of applications, and they all have ton of third-party libraries (think Spring, Hibernate, etc.) - you will end up with larger PermGen consumption, which might be exhausted after N applications. Placing shared libraries in the Tomcat shared folder might help with memory sizing issues, but then you face the upgrade lifecycle issue. You will need to coordinate the application upgrade properly. Also, you might end up with weird errors - because frameworks might share some objects statically, and that's not what your intent was, etc. Thus, using shared libraries need to be carefully planned. Usually, benefits of shared libraries are not worth the trouble, so we end up packaging each application separately. Shared libraries can be very useful when admins want to enforce library versioning, and force developers to use given environment, rather than them including what they want/need. It's an architectural decision, not so much performance optimization decision. > I read as much as I can but I'm stuck trying to find the best tools to > monitor the system and tackle memory issues (such as the dreaded PermGen). > I think it's a quite common scenario for a relatively small production > environment but I don't find the best configuration that suits this type of > deployment. > > Well, you probably want to profile your application(s) and see how they perform under various configuration options (memory sizing, connector sizing, etc). That gets much easier when you have all apps segmented to different environments. Your HTTPD setup helps a lot, as your clients don't care where HTTPD sends the traffic in the backend, to two instances or to twenty-eight instances. There might be minimal or insignificant performance overhead in maintaining 2 or 28 backend Tomcat instances connections. However, I would probably want to measure that too and see how it behaves under real-life like traffic. > Any help would be much appreciated. > > Thanks very much in advance > > Hope these questions give you something to think about and revisit and justify your choices. Cheers! Neven
