Guide for managing netLD servers installed in an Active-Active redundant configuration.


This document will explain the steps required to convert a slave into a master instance.


Overview

  • radmin command
  • Viewing Status
  • Convert Slave to Master
  • Convert Master to Slave


radmin command

The radmin command (found at /usr/share/netld/radmin) can be used to manage and check the status of a redundant server.

 

 Command  Description
radmin master Converts the current instance into the master server
radmin slave Converts the current instance into the slave server
radmin standalone Converts the current instance into a standalone server (disables redundancy)
radmin status Checks the current status of redundancy


Viewing Status

The radmin status command can be used to check the current status of redundancy.


To view the current status run the following commands: 

[root@server ~]# cd /usr/share/netld
[root@server netld]# ./radmin status


 Output Field  Description
Role Shows the current redundancy role of the server ("master", "slave", or "standalone")
Replication Shows whether or not redundancy is configured
PostgreSQL Shows the current status of the PostgreSQL configuration.
When the master and slave are connected this also shows the most recent PostgreSQL WAL ID  
Slave Host For a master instance this is the IP address of the currently configured slave


Master status, streaming to slave

[root@master netld]# ./radmin status
Role: master
Replication: configured
PostgreSQL: configured (streaming: 0/300D800)
Slave Host: 10.0.0.210
[root@master netld]#

In this output you can see a Slave Host is set and PostgreSQL is configured for replication. You can also see the current WAL ID in the PostgreSQL database.


Slave status, streaming from master  

[root@slave netld]# ./radmin status
Role: slave
Replication: configured
PostgreSQL: configured (streaming: 0/300D800)
Master Host: 10.0.0.209
[root@slave netld]#

This output shows the Master Host is set as well as the most recent WAL id. You can see that the WAL ID for the slave database (0/300D800) matches identically to the master server's status above. This indicates that the databases are in sync and all data is replicated. For a busy server this ID can change rapidly so they might not always be identical.


Master status, slave not running

[root@server ~]# cd /usr/share/netld
[root@server netld]# ./radmin status
Role: master
Replication: configured
PostgreSQL: configured (not streaming)
Slave Host: 10.0.0.210 

This output indicates that the database replication is not active ("not streaming"). This could either mean that the slave's postgresql server is not running, or that there is a communication problem between the two databases.


No redundancy configured

[root@server netld]# ./radmin status
Role: standalone
Replication: not configured
PostgreSQL: not configured

 In this output you can see that the netLD is configured as a standalone server and PostgreSQL is not in use. 

  

Convert Slave to Master

If the original master server is down, a slave server can easily be converted into the new master server by using the radmin master command


The following commands can be used to convert the slave server to a master server: 

[root@slave ~]# service netld stop
[root@slave ~]# service netld-pgsql stop
[root@slave ~]# cd/ usr/share/netld
[root@slave netld]# ./radmin master
Enter slave server IP address: ***.***.***.***
[root@slave netld]# service netld-pgsql start
[root@slave netld]# service netld start

  

Convert Master to Slave

A existing master server can be converted to a slave server using the radmin slave command.


The following commands can be used to convert a master server into a slave server:  

[root@server ~]# cd /usr/share/netld/
[root@server netld]# service netld stop
[root@server netld]# service netld-pgsql stop
[root@server netld]# ./radmin slave
Enter master server IP address: ***.***.***.***
This operation is destructive.
Any existing database will be removed and replaced with the contents of the specified backup file.
Are you sure you want to continue? [y/n] y
Enter password for Net LineDancer user 'admin' at 10.0.0.210: <password>
Executing system backup on master server..................
System backup complete.
Retrieving database from master...
Downloading... 100%
Applying backup to local server...
Archive:  tmp/backup_import.zip
   creating: lucene/
   creating: lucene/configurations/
 <............ cut for brevity ...............>
  inflating: pgsql/data/backup_label
Import complete.
[root@server netld]# service netld-pgsql start
[root@server netld]# service netld start