Automating failover situations can benefit an organization along with the database administrator who is on call. This article discusses how to setup Keepalived and how it may help in automated failovers for a Multi-Master MySQL cluster.
Last month was all about setting up your Multi-Master
MySQL cluster and keeping your standby master hot. This article is an
extension of our Multi-Master configuration and talks about great techniques to
automate a failover. There are several ways automating failover situations can
benefit an organization along with the database administrator who is on call.
This post discusses a simple setup of keepalived in moderate detail, and
how it may help in automated failovers for a Multi-Master MySQL cluster.
What
is Keepalived
Keepalived is a
utility that provides interface failover, in our case one virtual IP, and can
perform health checks. In the MySQL world, when using Multi-Master replication,
this is a very good mechanism to have. With a good implementation of Keepalived
you will be able to fail over a virtual/floating IP address when the master
(write) server becomes unavailable and switch that IP over to the hot standby
server.
Lets
Set it Up
If you have never installed keepalived please follow the steps below.
1. Get the tarball.
# wget http://www.keepalived.org/software/keepalived-1.1.20.tar.gz --2010-08-19 10:47:35-- http://www.keepalived.org/software/keepalived-1.1.20.tar.gz Resolving www.keepalived.org... 188.165.36.82 Connecting to www.keepalived.org|188.165.36.82|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 233002 (228K) [application/x-gzip] Saving to: `keepalived-1.1.20.tar.gz' 100%[======================================================================================>] 233,002 233K/s in 1.0s 2010-08-19 10:47:37 (233 KB/s) - `keepalived-1.1.20.tar.gz' saved [233002/233002]
2. Untar and unzip the file.
# /usr/local/src#tar xzvf keepalived-1.1.20.tar.gz
3. cd to the newly created directory.
# /usr/local/src#cd keepalived-1.1.20
4. Make sure you have at a minium openssl-devel installed
on your server.
# /usr/local/src/keepalived-1.1.20#yum install openssl-devel.x86_64
4a. If you want them all please run the following.
yum -y install kernel-headers kernel-devel
5. Configure keepalived.
# /usr/local/src/keepalived-1.1.20#./configure checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking for a BSD-compatible install... /usr/bin/install -c checking for strip... strip checking how to run the C preprocessor... gcc -E checking for grep that handles long lines and -e... /bin/grep checking for egrep... /bin/grep -E checking for ANSI C header files... yes checking for sys/wait.h that is POSIX.1 compatible... yes checking for uname... yes … configure: creating ./config.status config.status: creating Makefile config.status: creating genhash/Makefile config.status: creating keepalived/core/Makefile config.status: creating keepalived/include/config.h config.status: creating keepalived.spec config.status: creating keepalived/Makefile config.status: creating lib/Makefile config.status: creating keepalived/vrrp/Makefile Keepalived configuration ------------------------ Keepalived version : 1.1.20 Compiler : gcc Compiler flags : -g -O2 Extra Lib : -lpopt -lssl -lcrypto Use IPVS Framework : No IPVS sync daemon support : No Use VRRP Framework : Yes Use Debug flags : No
6. Run Make.
# /usr/local/src/keepalived-1.1.20#make make -C lib || exit 1; make[1]: Entering directory `/usr/local/src/keepalived-1.1.20/lib' gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c memory.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c utils.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c notify.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c timer.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c scheduler.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c vector.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c list.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c html.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c parser.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c signals.c gcc -g -O2 -I. -Wall -Wunused -Wstrict-prototypes -c logger.c … gcc -g -O2 -I/usr/src/linux/include -I../include -I../../lib -Wall -Wunused -Wstrict-prototypes -D_KRNL_2_6_ -D_WITHOUT_LVS_ -D_WITHOUT_IPVS_SYNCD_ -c vrrp_track.c … make[2]: Leaving directory `/usr/local/src/keepalived-1.1.20/keepalived/vrrp' Building ../bin/keepalived strip ../bin/keepalived Make complete make[1]: Leaving directory `/usr/local/src/keepalived-1.1.20/keepalived' make -C genhash make[1]: Entering directory `/usr/local/src/keepalived-1.1.20/genhash' gcc -g -O2 -I/usr/src/linux/include -I../lib -Wall -Wunused -Wstrict-prototypes -c -o main.o main.c … Building ../bin/genhash strip ../bin/genhash Make complete make[1]: Leaving directory `/usr/local/src/keepalived-1.1.20/genhash' Make complete
7. Make install.
# /usr/local/src/keepalived-1.1.20#make install make -C keepalived install make[1]: Entering directory `/usr/local/src/keepalived-1.1.20/keepalived' install -d /usr/local/sbin install -m 700 ../bin/keepalived /usr/local/sbin/ install -d /usr/local/etc/rc.d/init.d install -m 755 etc/init.d/keepalived.init /usr/local/etc/rc.d/init.d/keepalived install -d /usr/local/etc/sysconfig install -m 755 etc/init.d/keepalived.sysconfig /usr/local/etc/sysconfig/keepalived install -d /usr/local/etc/keepalived/samples install -m 644 etc/keepalived/keepalived.conf /usr/local/etc/keepalived/ install -m 644 ../doc/samples/* /usr/local/etc/keepalived/samples/ install -d /usr/local/share/man/man5 install -d /usr/local/share/man/man8 install -m 644 ../doc/man/man5/keepalived.conf.5 /usr/local/share/man/man5 install -m 644 ../doc/man/man8/keepalived.8 /usr/local/share/man/man8 make[1]: Leaving directory `/usr/local/src/keepalived-1.1.20/keepalived' make -C genhash install make[1]: Entering directory `/usr/local/src/keepalived-1.1.20/genhash' install -d /usr/local/bin install -m 755 ../bin/genhash /usr/local/bin/ install -d /usr/local/share/man/man1 install -m 644 ../doc/man/man1/genhash.1 /usr/local/share/man/man1 make[1]: Leaving directory `/usr/local/src/keepalived-1.1.20/genhash'
8. Type the following commands to create the service and
run level:
# cd /etc/sysconfig # ln -s /usr/local/etc/sysconfig/keepalived . # cd /etc/rc3.d/ # ln -s /usr/local/etc/rc.d/init.d/keepalived S100keepalived # cd /etc/init.d/ # ln -s /usr/local/etc/rc.d/init.d/keepalived
The
Configuration Files
Locate the main keepalived configuration file in the /usr/local/etc/keepalived
directory. The file name should be obvious but if not then look for
keepalived.conf. I like to make a backup of this file so I have something to
reference quickly if I need it but this is not necessary.
The configuration file on the master (write) server will be slightly
different from the configuration file on the slave (read) server. Below are the
two example files:
MASTER CONFIGUTATION FILE
! Configuration File for keepalived
global_defs {
router_id MYTEST
}
vrrp_instance VI_1 {
state MASTER
interface bond0
virtual_router_id 41
priority 101 # note the difference between the two servers
advert_int 1
authentication {
auth_type PASS
auth_pass 1111 # put in your own numeric password here (In this example it's 1111)
}
virtual_ipaddress {
192.168.1.102
}
}
SLAVE CONFIGURATION FILE
! Configuration File for keepalived
global_defs {
router_id MYTEST
}
vrrp_instance VI_1 {
state MASTER
interface bond0
virtual_router_id 41
priority 100 # note the difference between the two servers
advert_int 1
authentication {
auth_type PASS
auth_pass 1111 # put in your own numeric password here (In this example it's 1111)
}
virtual_ipaddress {
192.168.1.102
}
}
After you have implemented the configuration files, you should symlink them
over to the /etc/keepalived directory. This is where the /etc/init.d/keepalived
script looks for the configuration file.
# cd /etc/keepalived # ln -s /usr/local/etc/keepalived/keepalived.conf .
You are now ready to start keepalived on the master server but before we do that,
you should check the output of the following for reference:
# /sbin/ip addr show bond0 |grep inet inet 192.168.1.100/23 brd 192.168.1.1 scope global bond0
Start keepalived by running the following on both the master and slave
server. Start the master server first then the slave server.
# /etc/init.d/keepalived start Starting keepalived: [ OK ]
You can check to see if the IP has been added to bond0 by running the ip
addr line again.
Example for the Master server:
# /sbin/ip addr show bond0 |grep inet inet 192.168.1.100/23 brd 192.168.1.1 scope global bond0 inet 192.168.1.102/32 scope global bond0
You can also check /var/log/messages for good information about keepalived.
Example for the Master server:
19 20:27:38 sandbox Keepalived: Starting VRRP child process, pid=10521 19 20:27:38 sandbox Keepalived_vrrp: VRRP sockpool: [ifindex(7), proto(112), fd(9,10)] 19 20:27:39 sandbox Keepalived_vrrp: VRRP_Instance(VI_1) Transition to MASTER STATE 19 20:27:40 sandbox Keepalived_vrrp: VRRP_Instance(VI_1) Entering MASTER STATE 19 20:27:40 sandbox Keepalived_vrrp: VRRP_Instance(VI_1) setting protocol VIPs. 19 20:27:40 sandbox Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on bond0 for 192.168.1.102 19 20:27:45 sandbox Keepalived_vrrp: VRRP_Instance(VI_1) Sending gratuitous ARPs on bond0 for 192.168.1.102
Example for the Slave server:
19 20:30:23 sandbox2 Keepalived_vrrp: Using LinkWatch kernel netlink reflector... 19 20:30:23 sandbox2 Keepalived_vrrp: VRRP sockpool: [ifindex(7), proto(112), fd(9,10)] 19 20:30:24 sandbox2 Keepalived_vrrp: VRRP_Instance(VI_1) Transition to MASTER STATE 19 20:30:24 sandbox2 Keepalived_vrrp: VRRP_Instance(VI_1) Received higher prio advert 19 20:30:24 sandbox2 Keepalived_vrrp: VRRP_Instance(VI_1) Entering BACKUP STATE
Testing
We can test our setup with a very simple ping. First, you will need to have
three shells open, one to the master server, one to the slave server and one
running a ping to the virtual IP 192.168.1.102. While the ping is running, you
can simply stop keepalived and watch as the virtual IP flips over to the slave
server. You should use the same techniques described above to check if the
virtual IP has switched over to the slave server.
A ping test is the easiest way to test if the failover is going to work but
it is NOT the only test you need to run. Running a simple BASH script that
connects to MySQL on the Virtual IP (192.168.1.102) is a good way to test. Here
is a VERY simple test for mysql:
# while true; do mysql -usomeuser --host=192.168.1.102 --port=3306 -e "select 1"; sleep .5; done
So instead of running a ping, run the following script and see what the
results are. I would expect that the Virtual IP would be flipped over to the
slave server and the script above would not error out. Note that this is a very
simple test and if you are implementing keepalived in production, you should
test with your production load.
As always, millage may vary and there are defiantly other ways to accomplish
automated failovers to accomplish HA in MySQL.
