I have one master and one slave memcachedb servers. I need some java client to memcache db with such opportunities:
At first it establishes connection to master server. In case if master fails the slave should become master and java client should reconnect to him. After the first server repairs they must work again in replication.
So, can you please help me to choose the best java client for memcachedb with such requirements?
Regards, Evgeniy
Spring Framework should contain support for memcached through the caching module. I know EhCache is supporter. If you are in Java, EHCache might be worth a look as it does not require that extra install process as memcached. Also, if Spring doesn't have an adapter, it should be simple to provide one to it, allowing you to switch caching implementations dynamically without changing code.
I have used xmemcached as a java client with several Memcached Servers working in paralell. (Not Master/Slave(
Just one question, when you say Memcached DB which is the purpose of using Memcached? A cache or a database?
Finally, I haven't found any solutions to work with several servers in replication mode. So if you want to have the same data on several nodes you should add it manually. Also in case of some server failure you should manually reconnect to another one.
Please, let me know if you found better solution.
Regards, Evgeniy
Related
I would like to know if Servlet specifications provides a way to load http sessions into my web application.
The idea is simple : every time a new http client is connected, a new session is created... and I will send this session and its values into a database (for the time being this step is easy to do).
If this "master server" dies, another machine will take its IP address, so http clients will now send their requests to this new machine (lets call it "slave server").
Here I would like my slave server retrieve sessions from the old server... but I don't know which method from Servlet specifications can "add" session ! Is there a way to do it ?
PS: it's for an university project, so I cannot use already existing modules like Tomcat's mod_jk for this homemade load-balancer.
EDIT:
I think that a lot of people think I am crazy to not use already existing tools. It's an university project, and I have to make it with my bare hands in order to show to my professors the low level mecanisms that I have used. I already know it would be crazy to use what I am doing in production, when this project will be finished, it will be thrown in the trash.
For the moment, I didn't find a "standard way" to make it with the Servlet specifications, but I can maybe do it with Manager and Session from Tomcat native classes... How can I get the instances for those interfaces ?
This isn't exactly a new idea and is called session replication. There are a couple of ways to do this. The easiest ones imho are (in ascending order of preference):
Jetty's Session clustering with a database
Tomcat's Session clustering. I personally prefer the BackupManager, which makes sure that a session lives on 2 servers in a cluster at any given point in time and forwards clients accordingly. This reduces the network traffic for session replication to a bare minimum.
Session replication with a distributed cache like hazelnuts or ehcache. There are plugins for both jetty and Tomcat to do this. Since most often a cache is used anyway, this is to be the best solution for me. What I tend to do is to put 2 round robin balanced varnish servers in front of such a cluster, which serve the dual purpose role of load balancing the cluster and serving static content from in memory cache.
As for your university project, I'd turn in an embedded jetty with automatic session replication which connects to other servers via broadcast using hazelcast. Useful, not overcomplicated (iirc, you need to implement 2 relatively simple interfaces), yet powerful. Put a varnish in front of your test machines and you should be good to go.
This feature is supported by all major Java EE application server vendors out of the box, so you shouldn't implement anything by yourself. As Markus wrote it is referred as session replication or session persistence. You can take a look at WebSphere Liberty which is available for free for development. It supports it out of the box, without need to implement anything. You just need to:
install Liberty Download just the Liberty profile runtime
configure session replication Configuring session persistence for the Liberty profile
install and configure IBM Http Server for load balancing Configuring a web server plug-in for the Liberty profile
I've an app which is deployed on to a cluster with 2 jvms. The web application has cache implemented using Mbeans and the cache runs on each jvm. the cache is refreshed with a request pattern */refresh. The problem is that when the request goes through ODR, it routes it to only one server and the cache for only one server is refreshed. How do I solve this problem? Cache replication? I think it might be lot of work to implement cache replication. Any other solutions? Websphere api's ?
if I get the current instance of the application, I'm thinking of using AdminClient to get the clusters and then call the request on all the nodes on which the application is installed except for the current instance.
The Websphere way to do this is to use the DynaCache feature with DRS. The DynaCache is a kind of a hashmap, which can be distributed across the DRS cluster members. The dynacache has an API, DistributedMap, which extends the java.util.Map.
There are also a lot of configuration (Through AdminConsole and cachespec.xml) and monitoring possibilities (PMI with TPV).
Technical overview:
http://pic.dhe.ibm.com/infocenter/lnxinfo/v3r0m0/index.jsp?topic=%2Fliaag%2Fcache%2Fpubwasdynacachoverview.htm
DistributedMap API
http://pic.dhe.ibm.com/infocenter/adiehelp/v5r1m1/index.jsp?topic=%2Fcom.ibm.wasee.doc%2Finfo%2Fee%2Fjavadoc%2Fee%2Fcom%2Fibm%2Fwebsphere%2Fcache%2FDistributedMap.html
A good article from developerworks
http://www.ibm.com/developerworks/websphere/library/techarticles/0906_salvarinov/0906_salvarinov.html
The crude way we did something similar was to directly hit each Web Container on its own port. If you're able to reach them, that is.
Give me advice. I have one Java application server, and 5 servers where it is installed (for spread the load). To use a SQL database, and Hibernate. I want to receive information,information is not dependent on the server - making it common for all. how can I make it?
You have to use Load Balancing with Sticky Session. Which server are you using ?
We have a distributed architecture where our application runs on four Tomcat instances. I would like to know the various options available for communicating between these Tomcat instances.
The details : Say a user sends a request to stop listening to the incoming queues, this needs to be communicated with other Tomcat instances so that they stop their listeners as well. How can this communication be made across Tomcats?
Thanks,
Midhun
Looks like you are facing coordination problem.
I'd recommend you to use Apache ZooKeeper for this kind of the problems.
Consider putting your configuration to the ZooKeeper. ZooKeeper allows you to watch for the changes and if configuration was changed in ZooKeeper tomcat instance will be notified and you can adjust the behavior of your application on every node.
You can use any kind of external persistent storage to solve this problem, though.
Other possible way is to implement communication between tomcat nodes by yourself but in this case you'll have a problem with managing your deployment topology: every tomcat node should know about other nodes in the cluster.
what lies on the surface is RMI, HTTP requests. As well, IMHO, you could try to use MBeans. One more thing, you could use some non-java related things, like DBus or something, or even flat files... if all tomcats run on the same machine. Lots of options...
We use Hazelcast for this kind of scenario. They have an handy Http Session Clustering
The title pretty much says it all, but here's some background.
We have a database configured in glassfish accessed by a website deployed on glassfish, we also access the database from an external java application, it occurred to me that this could be somewhat inefficient since we open quite a few connections to the database from our external app. So I was wondering if we could somehow access he database through glassfish's connection pool?
Thanks in advance.
Piers
You'll have to try this.
http://javahowto.blogspot.com/2006/08/access-glassfish-datasource-remotely.html suggests it is possible to look up the connection pool via JNDI from a standalone client. An actual client code example is given at http://javahowto.blogspot.com/2006/08/access-jboss-datasource-remotely-from.html#client
That would only be possible if your external application was running in the same VM as glassfish. The word "external" says: Nope, not possible.
Note that databases are designed to handle lots of connections. That's one of the main reasons why they exist: To allow several programs at once to work on the same data.
I don't think you can access the pool, if your program does not run on glassfish.
A few connections to the database shouldn't matter too much, at least if the aren't created and destroyed very often. You could build a pool in your external application as well, if that is the case.
Well I'm answering my own question, and it's not a brilliant answer but it does sort of fulfil the requirements of my question.
What you can do is connect to an EJB from an external java application, if the bean provides access to your database then by using it you will be making use of the connection pooling provided by glassfish.
You can find info on how to do this
here - https://glassfish.dev.java.net/javaee5/ejb/EJB_FAQ.html
In terms of efficiency I'm not sure if this is a good idea since it may put excess strain on your web application, in my initial idea I was thinking to bypass the webapp completely and communicate directly with glassfish, any comments on this would be appreciated.
Another option is to add a web service to your Glassfish data access object.
You could then access the database with SOAP or REST calls.