Thursday, August 4, 2016

Fix issues in upgrading Ubuntu 14.04 to 16.04

When I upgraded my Ubuntu 14.04 PC to 16.04 it restarted and terminal screen was loaded without any GUI. I fixed this by doing following steps.

  • First login with by entering login name(this is your username) and password
  • Run sudo apt-get update
  • If above step fails run the command which is given in the error. Usually this is something related to dpkg.
  • Run sudo apt-get upgrade -f
  • If confirmations occurs while upgrading accept all
After upgrading is done restart the computer.

If it still goes to terminal run sudo do-release-upgrade

Friday, June 19, 2015

Accessing all highcharts in a page at once

Recently I needed to call a reflow method of all hi-charts in the page for a particular event. I used following method for that.

function redrawHighcharts() {
    for (var i = 0; i < Highcharts.charts.length; i++) {

Monday, May 11, 2015

Fixing Unicode issues in Pentaho CDA

Recently I encountered problem when sending a query parameter with unicode text to Pentaho CDA. For these type of queries CDA returns an empty result set although there are matching items. After some research I fixed this issue by adding an additional parameter to the JDBC connection url. Now JDBC connection is like below.

        <Connection id="1" type="sql.jdbc">

Saturday, March 14, 2015

Creating a Pentaho BI server cluster

Note - This is applicable to Pentaho BI server community edition 5.x only.

Pentaho BI server provides a large set of features which are essential for  BI applications. To use this in production we might need to create a CDA cluster to maintain high availability as well as load balancing.
To create a cluster we need to configure BI server instances to use a common data source to store configurations. I configured the following setup for this.

Follow these steps to create the cluster.

  1. Install MySQL servers and setup master master replication.
  2. Make sure you have installed Oracle Java 7 in all nodes. Using other java versions will cause runtime errors.
  3. Follow this document to to install a CDA instance. Make sure to follow the document named "Install with Your Own BA Repository" and follow the configurations related to MySQL. 
  4. Start the server and install all the components needed.
  5. Modify the cluster documentation as mentioned in this document.
    1. This document is missing the information related Quartz clustering with MySQL. Only PostgresQL configuration is there. Use the following configuration instead.
      1. #_replace_jobstore_properties
        org.quartz.jobStore.misfireThreshold = 60000
        org.quartz.jobStore.driverDelegateClass = org.quartz.impl.jdbcjobstore.StdJDBCDelegate
        org.quartz.jobStore.useProperties = false
        org.quartz.jobStore.dataSource = myDS
        org.quartz.jobStore.tablePrefix = QRTZ5_
        org.quartz.jobStore.isClustered = true
        org.quartz.jobStore.clusterCheckinInterval = 20000
    2. When configuring Jackrabbit clustering replace unique ID  in<Cluster id="Unique_ID"> with a ID like CDA1.
  6. Recompress the CDA folder and copy it to all other nodes.
  7. Extract the file and replace unique ID  in<Cluster id="Unique_ID"> accordingly. eg- CDA2, CDA3
  8. Start each node and make sure there are no error logs in tomcat/logs/pentaho.log.
  9. Make sure all CDA changes are replicated between cluster nodes.
  10. When configure the ELB make sure to enable sticky sessions.
  11. Alerts should be set to monitor CDA instances as well as MySQL replication.

Sunday, February 15, 2015

Deploying a HA Redis setup

Sentinel process takes the responsibility of electing a slave as master if a failure occurs. For more information refer  this.
  • Install Redis in each node. Following methods can be used to install Redis.
    1. Using Ubuntu repositories. 
      1. sudo apt-get install redis-server
    2. Manual installation
      1. You can download a Redis distribution from this page Follow the instructions on this page to setup Redis using the downloaded setup
  • Set requirepass property to set the password in the configuration file in /etc/redis. Note that this should be same in all nodes.
  • Set Up replication
    1. Set the following properties to set replication on slaves.
      1. slaveof <masterip> <masterport>
      2. masterauth <master-password> //The same password we used previously
    2. Set masterauth property also in the master in case of master goes down and later joins as a slave (Once a slave is elected as a master).
  • To test whether the replication is working, log in to redis console of the master using redis-cli command and add a data. Log in to all slaves and see the entered data is there.
  • Setup sentinel in each node
    1. create a file named sentinel.conf where your redis configurations exists.
    2. add the following content to sentinel.conf (change values according to your setup). 
      1. sentinel monitor mymaster <ip> <port> 2
        sentinel down-after-milliseconds mymaster 60000
        sentinel failover-timeout mymaster 180000
        sentinel parallel-syncs mymaster 1
        It tells Redis Sentinel that the master is <ip>, the master's name is "mymaster", and  start failover if more than two Redis Sentinel has detected the master failed.
  • Start sentinel process in each node using the following command.
    sudo redis-sentinel <path to the configuration file> &
    To stop a sentinel process use the following command.
    sudo redis-sentinel <path to the configuration file> shutdown
  • To test failover you can kill master process and see still you can write to the cluster using your client application. Not that when master changes sentinel will rewrite the redis configurations in each node. To get back to the original state you will have to revert back the changes.

  • How to access above setup programmatically.

    I will be using Java with Jedis library for this example. 
    HashSet<String> sentinels = new HashSet<>();
    JedisPoolConfig jedisPoolConfig = getJedisPoolConfig();
    String[] nodes = //This should contain addresses to sentinel processes;
    for (String node : nodes) {
    pool = new JedisSentinelPool(getConfig(sentinelMasterKey), sentinels, jedisPoolConfig);
    Jedis jedis = pool.getResource();
    jedis.set(key, value);

    private JedisPoolConfig getJedisPoolConfig() { JedisPoolConfig jedisPoolConfig = new JedisPoolConfig(); if (application().configuration().getInt("redis.pool.maxIdle") != null) { jedisPoolConfig.setMaxIdle(application().configuration().getInt("redis.pool.maxIdle")); } if (application().configuration().getInt("redis.pool.minIdle") != null) { jedisPoolConfig.setMinIdle(application().configuration().getInt("redis.pool.minIdle")); } if (application().configuration().getInt("redis.pool.maxTotal") != null) { jedisPoolConfig.setMaxTotal(application().configuration().getInt("redis.pool.maxTotal")); } if (application().configuration().getInt("redis.pool.maxWaitMillis") != null) { jedisPoolConfig.setMaxWaitMillis(application().configuration().getInt("redis.pool.maxWaitMillis")); } if (application().configuration().getBoolean("redis.pool.testOnBorrow") != null) { jedisPoolConfig.setTestOnBorrow(application().configuration().getBoolean("redis.pool.testOnBorrow")); } if (application().configuration().getBoolean("redis.pool.testOnReturn") != null) { jedisPoolConfig.setTestOnReturn(application().configuration().getBoolean("redis.pool.testOnReturn")); } if (application().configuration().getBoolean("redis.pool.testWhileIdle") != null) { jedisPoolConfig.setTestWhileIdle(application().configuration().getBoolean("redis.pool.testWhileIdle")); } if (application().configuration().getLong("redis.pool.timeBetweenEvictionRunsMillis") != null) { jedisPoolConfig.setTimeBetweenEvictionRunsMillis(application().configuration().getLong("redis.pool.timeBetweenEvictionRunsMillis")); } if (application().configuration().getInt("redis.pool.numTestsPerEvictionRun") != null) { jedisPoolConfig.setNumTestsPerEvictionRun(application().configuration().getInt("redis.pool.numTestsPerEvictionRun")); } if (application().configuration().getLong("redis.pool.minEvictableIdleTimeMillis") != null) { jedisPoolConfig.setMinEvictableIdleTimeMillis(application().configuration().getLong("redis.pool.minEvictableIdleTimeMillis")); } if (application().configuration().getLong("redis.pool.softMinEvictableIdleTimeMillis") != null) { jedisPoolConfig.setSoftMinEvictableIdleTimeMillis(application().configuration().getLong("redis.pool.softMinEvictableIdleTimeMillis")); } if (application().configuration().getBoolean("redis.pool.lifo") != null) { jedisPoolConfig.setLifo(application().configuration().getBoolean("redis.pool.lifo")); } if (application().configuration().getBoolean("redis.pool.blockWhenExhausted") != null) { jedisPoolConfig.setBlockWhenExhausted(application().configuration().getBoolean("redis.pool.blockWhenExhausted")); } return jedisPoolConfig; }

    Thursday, February 5, 2015

    Bind a remote server's port to a local port

    If you have a remote server (say in Amazon EC2) you might want to access a particular port of that server. But there can be situations where it is not that port is not globally open. If you do not want to bother making it globally open you can use it by binding it to a local port of your workstation via ssh. Following command will bind port 9000 of remote machine to your local port 8000.  As an example if it is web server you can easily access it by typing localhost:8000 in your web browser.

    ssh -L 8000:localhost:9000 username@host

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

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