How Ganglia works


What is Ganglia ?

Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and Grids. It is based on a hierarchical design targeted at federations of clusters. It leverages widely used technologies such as XML for data representation, XDR for compact, portable data transport, and RRDtool for data storage and visualization.

ganglia

Ganglia has the following main components:

1. Ganglia Monitoring Daemon (gmond)
Gmond stands for ganglia monitoring daemon. It is a lightweight service that is installed on every machine you’d like to monitor.
Gmond has four main responsibilities:

1.1 Monitor changes in host state.
1.2 Announce relevant changes.
1.3 Listen to the state of all other ganglia nodes via a unicast or multicast channel.
1.4 Answer requests for an XML description of the cluster state.

Each gmond transmits information in two different ways:

a. Unicasting or Multicasting host state in external data representation (XDR) format using UDP messages.
b. Sending XML over a TCP connection.

Notes about gmond:

– The main configuration file of gmond is /etc/gmond.conf
– gmond is multithreaded

Test gmond installation:

telnet localhost 8649

You should see XML that conforms to the ganglia XML spec.

Or

gmond -d 5 -c /etc/ganglia/gmond.conf

to see the service in debugging mode.

2. Ganglia Meta Daemon (gmetad)
The ganglia meta daemon (gmetad) is a service that collects data from other gmetad and gmond sources and stores their state to disk in indexed round-robin (RRD) databases. Gmetad provides a simple query mechanism for collecting specific information about groups of machines.

Notes about gmetad:

– the main configuration file for gmetad is /etc/gmetad.conf
– You need atleast one gmetad daemon installed node on each cluster.
– This gemetad daemon is the one who collects data send by gmond daemon.
– All other nodes other than the one in the cluster, do not require gmetad daemon to be installed.
– If you need the machine containing gmetad configured as node to be monitored, then in that case you need to install both gmond and gmetad on the machine.

Test gmetad installation:

telnet localhost 8651

3. Ganglia PHP Web Front-end
The Ganglia web front-end provides a view of the gathered information via real-time dynamic web pages. Most importantly, it displays Ganglia data in a meaningful way for system administrators and computer users using PHP.

how ganglia works

In this picture we can see  gmond installed in each node and sending data to gmetad installed in a “gmetad node”. We can have one or more  “nodes with gmetad” in a cluster.

gmetad collects all the data from gmond and stores it in rrdtool database. Which is then collected by the php scripts, and showed as the first picture in this article.

4. Gmetrics
The ganglia metric tool is a commandline application that you can use to inject custom made metrics about hosts that are being monitored by ganglia. It has the ability to spoof messages as coming from a different host in case you want to capture and report metrics from a device where you don’t have gmond running (like a network or other embedded device).

5. Gstat
The ganglia stat tool is a commandline application that you can use to query a gmond for metric information directly.

6. RRD tool:

Ganglia uses RRD tool to store its data and visualization.

RRD tool is the short form for Round Robin Data base tool. This is a wonderful and useful open source data base tool. In this RRD stores data in time-series. For example RRD tool will store all values of CPU load at a certain time interval and then graph these data according to time.

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sysadmin, developer, RHCSA
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