Production distributed system – pt. 2

Once we were able to have the Galera databases sync and aware of each other is was time to tackle the issue of “How do we register the service?”

So it was time to work on the Consul cluster, we considered using 3 different nodes for this cluster to add the another layer of redundancy to each component but the customer elected to run the Consul service on the same nodes as the Galera. It might seem like an odd point to have the discovery server run on the same node as the service is it monitoring, but the logic was “if the Galera node is down, then the Consul service is also degraded, and we will address them together”

So we build a 3 node Consul service, with agents on each of the Galera nodes.

each node was configured to join the cluster with 2 other nodes specified in the “start_join” directive

"server": false,
"datacenter": "foo",
"data_dir": "/var/consul",
"encrypt" : "",
"log_level": "INFO",
"enable_syslog": true,
"start_join": [ "","" ]

The file was located in the /etc/consul.d/client/config.json  this took care of the client/server sign up, but when about knowing if the Galera is up … Simple, we created a check that queries the backend database and reports back, this file , aptly named galera.json was located on the main /etc/consul.d   directory

"name": "galeradb",
"tags": ["icinga-galera"],
  "check": {
    "id" : "mysql",
    "name": "Check mysql port listening",
    "tcp" : "localhost:3306",
    "interval": "10s",
    "timeout": "1s"

this ensured that the Consul checked the response of the database and reported back to the cluster in case of a failure and make sure to allow election and deletion to the other nodes.

At this stage , then the backend was ready we started the Icinga installation, with 2 master and 2 web servers in a redundant connectivity (that documentation is found here ), and then we needed to configure the IDO to the Galera database, we hit an issue.

As we changed the /etc/resolv.conf on the Icinga nodes to use the 3 consul nodes , icinga use the Consul as the DNS and be able to resolve for the database:


* The db_ido_mysql library implements IDO functionality
* for MySQL.

library "db_ido_mysql"

object IdoMysqlConnection "ido-mysql" {
  user = ""
  password = ""
  host = "galeradb.service.consul"
  database = "icinga"

but considering that many checks of the system relied on DNS resolving of external IP’s .. we were stuck with how we can ensure that the service returned the correct IP.

So we had to connect Icinga  to a named server, in our case Bind9. We build a named service on the same nodes so we can make as little change on the icinga server and use the already configured DNS requests on port 53 [UDP] going to the consul servers to work for us.

A very basic named.conf :

options {
  directory "/var/named";
  dump-file "/var/named/data/cache_dump.db";
  statistics-file "/var/named/data/named_stats.txt";
  memstatistics-file "/var/named/data/named_mem_stats.txt";
  allow-query { any; };
  recursion yes;

  dnssec-enable no;
  dnssec-validation no;

/* Path to ISC DLV key */
  bindkeys-file "/etc/named.iscdlv.key";

  managed-keys-directory "/var/named/dynamic";

include "/etc/named/consul.conf";

Notice the inclusion of the consul.conf file , this is where the “magic” happens:

zone "consul" IN {
  type forward;
  forward only;
  forwarders { port 8600; };

This file tells named to forward all DNS request to external DNS server except for those with a “consul” domain , which are then forwarded to the localhost on port 8600 ( consul’s default DNS port) ,and thus provide the IP of the Galera cluster, for any other IP is will go to the DNS of choice configured when the consul service was build, we choose the all too familiar  “” ( this is added to the cluster bootstrap stage )


So the next stage was to test the resolving and the system survival.

Production distributed system – pt. 1

A customer came to AikiLinux requesting our assistance in designing and implementing a highly distributed and resilient monitoring system based on Icinga, with a planned scope of monitoring it’s own internal cloud service and for some of the services it provides for it’s external customers.

In the initial step we evaluated the requirements of the cluster and also build a small scale lab for them (master, 2 satellites and a host to monitor), and then set out to understand the network topology and limitations that might impact performance.

The things that we found were “normal” for a large multi continent organisation:

  • remote separated data centres
  • very restrictive IT department
  • ESX resources
    … nothing new or things we haven’t encountered before.

So we set out to design the solution and thought on what components will help us provide a truly redundant system, without relying on any cloud provider service, all done in house.

The Stack we ended up with was fairly simple : MariaDB Galera , HashiCorp Consul, Named for the database, and a standard HA setup for the Icinga itself.

The first challenge in building this system was ensuring that the Galera cluster was up and running so we modified the  /etc/my.cnf.d/server.cnf

# this is read by the standalone daemon and embedded servers

# this is only for the mysqld standalone daemon
# * Galera-related settings
# Allow server to accept connections on all interfaces.
innodb_locks_unsafe_for_binlog = 1

## Galera Cluster Configuration

and started the nodes….no sync between the master and the nodes.

We tested several solutions, modifying the security policy and the firewall, but in the end the only way to get the cluster up and running was to disable SElinux (mind you, it was after the 3rd firewall that you need to get through to gain access to the server) .

Once the node “saw” each other, we started testing data replication and we saw that 2 nodes replicate data but the 3rd did not.

It turns out that NTP was disabled and the time diff between the servers was more then 1900 seconds, uncomment the ntp records and ensure the sync of the clocks … and now we have replication. YAY!!




Updates and plans for the future

It has been a couple of busy months for our team at AikiLinux since FlossUK, with good things happening:

  • We have started working with Icinga on organising an Icinga Camp in Tel Aviv later this year, the provisional dates are 10-16 of December .
  • We have expanded our personel by bringing a new person to the fold in the UK.
  • As we strive to expand our knowledge, our team members have been working and have implemented a Prometheus monitoring solution at on of our customers, and also building a DR solution for their AWS  based on Terraform .
  • 2 new clients started the engagement with AikiLinux :

Terraform output , Ansible and Icinga

In the last several month Assaf have been (slowly) maintaining and working on updating and improving the Icinga2  Ansible playbooks , and as he worked on those he found that he needed the hosts to test on to be built and taken down in a fast repetition, and to preform the build and shutdown was too time consuming.

Welcome Terraform , the wonderful tool from HashiCorp has provided him with the ability to provision the server and remote nodes fast and in a reproducible way to ensure that each code run is tested in a clean and similar setup.

One issue was that the ‘Hosts’ file for the ansible run had to be manually changed each time with the new IP’s of the new instances ( AWS is nice for this short intervals) , and that slowed the progress down.

We know that many people are using ansible and terraform combination to manage their infrastructure, but in most cases the we found on line the ansible is called as a ‘local-exec’ provisioner at the end of the execution , and thus uses the internal variable’s of the terraform run, as we needed an external file for the testing ( for simulation of the user experience and the way the roles are looking at the inventory) it was important to create the inventory file in a specific way.

“Simple” most terraform users will say, “just use the provisioner ‘local-exec’ to write the output to a file” and they are correct, with a little caveat, if you wish to write the file in a specific resource creation order, you end up with a file that is out of order.
For example, here is an output file we got when building an icinga2 demo environment with a master and 2 nodes (webservers):

 [monitoring_servers]   # the Icinga roles need this group to know which are the master servers

This will cause our Ansible to read as if we have 3 master servers, and that of course is incorrect.

What the file should look like is


Do notice the group separator that is required/was added in the end, this was skipped in all the previous runs due to the order of creation, so to fix this issue the solution was very simple. ‘depends_on‘ which is a simple “wait” function that causes resources to wait for one to be ready.
In this case we wait for the server IP to be added and then we add the label and the IP’s of the nodes.

This solution has enabled us to speed out testing quite nicely and is a thing that should allow us to bring more improvements to the Ansible playbooks in a faster pace.

Engine migration

One of the customers we have has asked us to help evaluate alternative monitoring engines to the one they currently use (Nagios Core 4.1.1, complied from source) within their overall solutions, as an “easy to start” option we advised them to migrate to Icinga 1.x (although we explained to the client that the project has no active development to it, and is in maintenance mode only).

Understanding those issues and knowing that if they want to fully migrate to another solution they will have to either write it themselves or adapt to another openly available option, we implemented the latest Icinga 1 ( Icinga 1.14.0 ) within their solution and asked them to benchmark the behaviour of the system :

Application   Nagios Engine Icinga Engine
Main page Part I 14.31s 9.5
  Part II 12.72 9.32
Event Console   9.71s 12.1
Host Groups   21.25s 14.7
Outages   7.5s 8.19
System   9.71s 8.7


Stats: 20000 Hosts, 1 service check per host, As can be seen in most cases the Icinga engine outperformed the Nagios engine.

Icinga Camp Berlin

Speaking today at Icinga Camp Amsterdam

Icinga Camp Amsterdam 2016










Come Join us if you still can.

Will be a day full of Icinga cool talks