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Friday 15 February 2019

A Clustering Guide to CrateDB and ElasticSearch

Hi friends,

Recently I ran CrateDB in multi-node environment as a trial and in this post I'll share my findings as to what is the basic setup and configuration that is required to have high availability setup in CrateDB. I am pretty sure that similar settings will be useful for ElasticSearch as well.

I used crateDB version 3.2.2 and Java 8 for this POC.

So there is some bootstrap checks before the server runs successfully. According to the documentation those are some mandatory checks that are mandatory and needed to get the cluster running smoothly in multi-node environment. 

The first problem I faced was related to increasing ulimit in Ubuntu, which I have explained in this post - Increase Open Files/File Descriptors/Ulimit in Ubuntu | CrateDB ElasticSearch.

Once my CrateDB ran successfully, I began to mess around with basic settings and configurations. Remember, many of the things can be customised, and I'll share a few read-worthy links if you truly want to customise all settings around your cluster, towards the end of this post.

So here's the final configuration that worked for me:

Here's the explanation for the non-obvious ones:

Increase Open Files/File Descriptors/Ulimit in Ubuntu | CrateDB ElasticSearch

Hi friends,

This week I faced a rather peculiar issue while trying to setup clustering in CrateDB, which is very much similar to the clustering done in ElasticSearch. As soon as I did the basic configuration which you can find here, starting the process showed the following kinds of exceptions:

ERROR: bootstrap checks failed
max file descriptors [16384] for elasticsearch process is too low, increase to at least [65536]
max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]

java.lang.RuntimeException: bootstrap checks failed
initial heap size ... not equal to maximum heap size ...; this can cause resize pauses and prevents mlockall from locking the entire heap
please set [discovery.zen.minimum_master_nodes] to a majority of the number of master eligible nodes in your cluster
    at org.elasticsearch.bootstrap.BootstrapCheck.check(

[WARN ][o.e.b.BootstrapChecks    ] [node-1] max file descriptors [...] for elasticsearch process is too low, increase to at least [65536]
[WARN ][env ] max file descriptors [65535] for elasticsearch process likely too low, consider increasing to at least [65536]
[WARN ][o.e.b.BootstrapChecks    ] [node-1] max number of threads [1024] for user [] is too low, increase to at least [2048]
[WARN ][o.e.b.BootstrapChecks    ] [node-1] system call filters failed to install; check the logs and fix your configuration or disable system call filters at your own risk   

The second one which is related to heap size can be very easily solved by specifying HEAP params in environment variables of your system for CrateDB or ElasticSearch. You need to have the same heap size for -Xmx and -Xms. Something like:


The other one, max file descriptors, is related to ulimit set on your system. To see your existing hard and soft limits, use these commands in terminal:

$ ulimit -Hn
$ ulimit -Sn

In my case, hard limit was set to 4096 and soft limit was set to 1024 by default.
Also, using this option doesn't work in Ubuntu, atleast not in 18.04:
$ ulimit -n 70000
In order to solve the remaining issue related to max open files or increase file descriptors, just follow these steps and you will be good to go:

  • Go to the following file:

$ sudo vim /etc/security/limits.conf

  • Add the following lines in the file:

* soft nofile 80000

* hard nofile 80000

* soft nproc 80000

* hard nproc 80000

root soft nofile 80000

root hard nofile 80000
  • Save the changes.
  • Next you need to go to the following file:
$ sudo vim /etc/systemd/user.conf
  • Add this to the file and save changes:
  • Do the same in the following file:
$ sudo vim /etc/systemd/system.conf
These changes take care that the ulimit is increased for GUI based login.

Thursday 14 February 2019

Switch Between Multiple Java Versions on Linux

Hi friends,

In my previous blog post - Install Java 11 and Java 8 on Linux, I shared the way to install Java 11/Java 8 on your Linux machine. Now many of the current applications do not support Java 11 yet, so you must need a way to quickly switch between different installations of Java on your Linux machine. Without further ado, let's get started.

Way 1:

If you actually followed my way of installing Java 8/ Java 11 on your machine, and did set Java 8 / Java 11 default by using either of these commands:

sudo apt install oracle-java8-set-default

sudo apt install oracle-java11-set-default

Simply install the other command and it will automatically set that version as default in your system.

Now if you have both the above packages installed and now you want to set either of them as default, simply purge the one you wish to set as default and reinstall it.

So if you want to set Java 8 as default, run these commands in your terminal in order:

sudo apt purge oracle-java8-set-default

sudo apt install oracle-java8-set-default

If you want to set Java 11 as default, run these commands in your terminal in order:

sudo apt purge oracle-java11-set-default

sudo apt install oracle-java11-set-default

Way 2:

Sunday 10 February 2019

Install Java 11 and Java 8 on Linux

Hello friends,

As many of you must be knowing that Oracle officially ended the support for Java 8 in January this year. What this means for you? You get to try your hands on the latest JDK, which is 11.0.2 as of now. I will cover practical daily-code uses of Java 11 in a separate post soon. But till that time, let's discuss how to install Java 11 on your Linux distro. 

Now since many of your applications might still be using Java 8 and switching to Java 11 on production might not sound the best idea to your manager. This leaves you to find a way to install multiple Java versions on your machine and be able to switch between them in real-time.

In this post I'll share the steps to install Java 8 and Java 11 on your Linux machine and you can find how to switch between these two installations in this post -> How to switch between Java versions on Linux.