Sunday, September 7, 2014

Implementing session timeout in playframework

According to play documentation "There is no technical timeout for the Session. It expires when the user closes the web browser. If you need a functional timeout for a specific application, just store a timestamp into the user Session and use it however your application needs (e.g. for a maximum session duration, maximum inactivity duration, etc.)."

So I used the following way to implement a session timeout. Following custom authenticator class was used to implement this.

  public class ValidateUserSessionAction extends Security.Authenticator{

    @Override
    public String getUsername(Http.Context ctx) {
        long currentTime=System.currentTimeMillis();
        long timeOut=Long.parseLong(Play.application().configuration().getString("sessionTimeout")) * 1000 * 60;
        String temp=ctx.session().get(Constants.LAST_SEEN_KEY);
        if (temp == null) {
            temp = String.valueOf(currentTime);
        }
        if((currentTime-Long.parseLong(temp))<timeOut) {
            //If multiple instances are running, time should be synchronized between nodes
            ctx.session().put(Constants.LAST_SEEN_KEY, String.valueOf(System.currentTimeMillis()));
            return ctx.session().get(Constants.SESSION_USER_KEY);
        }else{
            ctx.session().clear();
            return null;
        }
    }

    @Override
    public Result onUnauthorized(Http.Context ctx) {
        return redirect(controllers.routes.UserController.signIn());
    }

    
}

Above authenticator class can be used to validate user actions like below.
 
 @Security.Authenticated(ValidateUserSessionAction.class)
    public static F.Promise<result< updateEmail() {
        //do something
        return ok();
    }

Saturday, September 6, 2014

Optimizing Apache Storm deployment

Recently we happen to run some pretty large Storm topologies in a Storm cluster which runs on Linux. When we running it there were two main issues occurred due to system limitations. First one was logged in Storm logs as,

“java.lang.OutOfMemoryError : unable to create new native Thread”.


We fixed this problem by increasing the Ulimit for Storm. Usually storm spawns processes with an user named Storm. So we have to increase the Ulimit for storm user. You can see the ulimits using command "ulimit -u". To increase the ulimits you can follow an approach like this.

The second problem was communication link failures between Storm nodes as well as communication link failures between other services (e.g. external APIs, databases, etc). To resolve this problem we had to enable tcp time wait reuse and also we increased the port range for tcp. hat can be done in following manner.

 Put these to /etc/sysctl.conf file and issue 'sysctl -f'
    net.ipv4.tcp_tw_reuse = 1
    net.ipv4.ip_local_port_range = 18000    65000

Note that we have to apply this setting for every node in Storm cluster. In addition to there were some errors like below due to Netty timeouts (Storm uses Netty as underlying messaging layer).

java.lang.RuntimeException: java.lang.RuntimeException: Client is being closed, and does not take requests any more
at backtype.storm.utils.DisruptorQueue.consumeBatchToCursor(DisruptorQueue.java:107) ~[storm-core-0.9.1.2.1.4.0-632.jar:0.9.1.2.1.4.0-632]
at backtype.storm.utils.DisruptorQueue.consumeBatchWhenAvailable(DisruptorQueue.java:78)

This can be corrected by increasing netty timeout values in configurations.

Friday, June 13, 2014

Introduction to Play-Framework modules

Play framework inherently support modularization. In other words we can develop play modules and reuse them in different play applications. This article provides a good guide on how to do that. But that is little bit outdated for latest Play distributions. I will describe the changes which is needed to be done to create a play module on latest play versions.
Playframework no longer has a play console. Instead of that it uses Typesafe activator. So you need to download activator and add activator to your environment path.
You can create boilerplate code for a play app using the  template called Just play java. In my case I needed to create a authentication module. So I created a Play action called auth in controllers package. Then to publish the module go the project directory and issue clean command. Then issue publish-local command. If it is successful you will get a output like this.

[info] published ivy to /home/prabhath/.ivy2/local/authmodule/authmodule_2.10/1.0-SNAPSHOT/ivys/ivy.xml
[success] Total time: 15 s, completed Jun 13, 2014 10:49:13 AM

Then create a new application which will use the previously created auth module. To add the dependency to new project update the build.sbt file. Content of my build.sbt file is like below.

name := """Test"""

version := "1.0-SNAPSHOT"

libraryDependencies ++= Seq(
  javaCore,  // The core Java API
  "junit" % "junit" % "4.8.2",
   "authmodule"%"authmodule_2.10"%"1.0-SNAPSHOT"
)

play.Project.playJavaSettings

Next you have to tell the path of your local repository to the application. To do that edit plugins.sbt file in /<your project>/project directory. I added the following line to plugins.sbt file.

resolvers += "Local Play Repository" at "file://home/prabhathp/.ivy2/local/"

Now build the project and you will be able to use the classes in your module/controllers package inside classes in your controllers. Note that you do not need to add imports when reusing module components.


Tuesday, April 22, 2014

Add a attachment to CouchDB with play framework JavaAPI

I tired to write a rest API which act as a mediator between clients and CouchDB API. This was done using Playframework's Java API. I wrote the following controller method which takes a POST request which contains file name, content-type and file to be stored as parameters and send as a PUT request to CouchDB.


   public static Result putAttachment(){
        Http.MultipartFormData body = request().body().asMultipartFormData();
        Http.MultipartFormData.FilePart picture = body.getFile("picture");
        String fileName=null;
        String contentType=null;
        File file=null;
        if (picture != null) {
            fileName = picture.getFilename();
            contentType = picture.getContentType();
            file = picture.getFile();
        } else {
            //TODO implement
        }
        String restServiceUrl = "http://127.0.0.1:5984/test/a/"+fileName;
        F.Promise<play.libs.WS.Response> future =play.libs.WS.url(restServiceUrl)
                .setContentType(contentType).setQueryParameter("rev","7-00e01f7f430649d984fc8488358a1953")
                .put(file);
        return Results.ok(future.get(50000000).getBody());
    }

Friday, April 18, 2014

Fixing Error "Failed to load VMMR0.r0 (VERR_SUPLIB_WORLD_WRITABLE)" in Virtualbox

Recently I  to installed Oracle Virtualbox on my Ubuntu 12.04 computer to run Hortanworks sandbox. When I am trying to start the Sanbox it gave me an error like this.

Failed to load VMMR0.r0 (VERR_SUPLIB_WORLD_WRITABLE).
Unknown error creating VM (VERR_SUPLIB_WORLD_WRITABLE).

What it says is /usr/bin forlder is world writable. Usually this is not world writable. But somehow I have unintentionally changed the permissions. I fixed this using the following command.

chmod o-w /usr/bin

Friday, February 21, 2014

Integrating an Akka.io actor system with Play framework (A distributed message classifier with Akka.io and Play framework)


Recently we developed a distributed message classifier. This can process rapid burst of text (email, twitter feeds, etc) and get results.


To implement the processing part we used Akka.io which is an event based distributed framework. Currently to analyse messages we use a web service. But any other processing mechanism (local or remote) can be easily plugged to this.
After implementing the core we needed to publish messages to the applications using REST. To do that we integrated it with Play Framework. Also I developed an admin panel using MVC features provided by it.
While integrating the existing actor system with play framework several conflicts occurred. One reason for this was Play framwork internally uses an actor system too. So I had to do several tweaks and change some configurations. I am not going to discuss each of them here because it will be too lengthy. This is the URL to our git-hub repo https://github.com/Buddhima/MessageClassifier. You can fork it and see those by your self. It has a very descriptive user guide and wiki which explains from architecture to UI. Hope this will be useful to starters who are trying to get familiarized with Akka.io and Play framework.

Thursday, November 14, 2013

Enable access from other hosts to a MySQL server

Recently I deployed a MySQL server. But there was a problem that I could not access the data base from a application which was hosted in another server. The reason for this is by default MySQL server does not accepts requests from other hosts except the localhost.
To solve this problem we have to do two tasks.


  • Create a user which has permissions to read and write to a database from a different host
GRANT ALL PRIVILEGES
ON database.*
TO ‘user’@'yourremotehost'
IDENTIFIED BY 'newpassword';

As an exmaple following query enables root user to access all the databases from any host.

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'password';

  • Bind the ip adress
To do this you have to edit the MySQL configuration file. In Ubuntu this is /etc/mysql/my.cnf
There you can find an entry like
bind-address = 127.0.0.1 

If you want to enable access from all the host just remove it. If you want to limit the hosts you can add entries like
bind-address = your ip

After doing that you have to restart the MySQL server. In Ubuntu you can do that like below.
sudo /etc/init.d/mysql restart