转载
Mysql Cluster: Two webserver setup (three servers required for true redundancy)
HOWTO set up a mysql cluster for two servers
Introduction
This HOWTO was designed for a classic setup of two servers behind a
loadbalancer. The aim is to have true redundancy - either server can be
unplugged and yet the site will remain up.
Notes
You MUST have a third server as a managment node but this can be shut
down after the cluster starts. Also note that I do not recommend
shutting down the managment server (see the extra notes at the bottom
of this document for more information). You can not run a mysql cluster
with just two servers And have true redundancy.
Although it is possible to set the cluster up on two physical servers
you WILL NOT GET the ability to "kill" one server and for the cluster
to continue as normal. For this you need a third server running the
managment node.
I am going to talk about three servers,
mysql1.domain.com 192.168.0.1
mysql2.domain.com 192.168.0.2
mysql3.domain.com 192.168.0.3
Servers 1 and 2 will be the two that end up "clustered". This would be
perfect for two servers behind a loadbalancer or using round robin DNS
and is a good replacement for replication. Server 3 needs to have only
minor changes made to it and does NOT require a mysql install. It can
be a low-end machine and can be carrying out other tasks.
STAGE 1: Install mysql on the first two servers:
Complete the following steps on both mysql1 and mysql2:
cd /usr/local/
http://dev.mysql.com/get/Downloa ... ux-gnu-i686.tar.gz/
from/
groupadd mysql
useradd -g mysql mysql
tar -zxvf mysql-max-4.1.9-pc-linux-gnu-i686.tar.gz
rm mysql-max-4.1.9-pc-linux-gnu-i686.tar.gz
ln -s mysql-max-4.1.9-pc-linux-gnu-i686 mysql
cd mysql
scripts/mysql_install_db --user=mysql
chown -R root .
chown -R mysql data
chgrp -R mysql .
cp support-files/mysql.server /etc/rc.d/init.d/
chmod +x /etc/rc.d/init.d/mysql.server
chkconfig --add mysql.server
Do not start mysql yet.
STAGE 2: Install and configure the managment server
You need the following files from the bin/ of the mysql directory:
ndb_mgm and ndb_mgmd. Download the whole mysql-max tarball and extract
them from the bin/ directory.
mkdir /usr/src/mysql-mgm
cd /usr/src/mysql-mgm
http://dev.mysql.com/get/Downloa ... ux-gnu-i686.tar.gz/
from/
tar -zxvf mysql-max-4.1.9-pc-linux-gnu-i686.tar.gz
rm mysql-max-4.1.9-pc-linux-gnu-i686.tar.gz
cd mysql-max-4.1.9-pc-linux-gnu-i686
mv bin/ndb_mgm .
mv bin/ndb_mgmd .
chmod +x ndb_mg*
mv ndb_mg* /usr/bin/
cd
rm -rf /usr/src/mysql-mgm
You now need to set up the config file for this managment:
mkdir /var/lib/mysql-cluster
cd /var/lib/mysql-cluster
vi [or emacs or any other editor] config.ini
Now, insert the following (changing the bits as indicated):
[NDBD DEFAULT]
NoOfReplicas=2
[MYSQLD DEFAULT]
[NDB_MGMD DEFAULT]
[TCP DEFAULT]
# Managment Server
[NDB_MGMD]
HostName=192.168.0.3# the IP of THIS SERVER
# Storage Engines
[NDBD]
HostName=192.168.0.1# the IP of the FIRST SERVER
DataDir= /var/lib/mysql-cluster
[NDBD]
HostName=192.168.0.2# the IP of the SECOND SERVER
DataDir=/var/lib/mysql-cluster
# 2 MySQL Clients
# I personally leave this blank to allow rapid changes of the mysql clients;
# you can enter the hostnames of the above two servers here. I suggest you dont.
[MYSQLD]
[MYSQLD]
Now, start the managment server:
ndb_mgmd
This is the mysql managment server, not maganment console. You should
therefore not expect any output (we will start the console later).
STAGE 3: Configure the storage/SQL servers and start mysql
On each of the two storage/SQL servers (192.168.0.1 and 192.168.0.2) enter the following (changing the bits as appropriate):
vi /etc/my.cnf
Enter i to go to insert mode again and insert this on both servers
(changing the IP address to the IP of the managment server that you set
up in stage 2):
[mysqld]
ndbcluster
ndb-connectstring=192.168.0.3# the IP of the MANAGMENT (THIRD) SERVER
[mysql_cluster]
ndb-connectstring=192.168.0.3# the IP of the MANAGMENT (THIRD) SERVER
Now, we make the data directory and start the storage engine:
mkdir /var/lib/mysql-cluster
cd /var/lib/mysql-cluster
/usr/local/mysql/bin/ndbd --initial
/etc/rc.d/init.d/mysql.server start
If you have done one server now go back to the start of stage 3 and repeat exactly the same procedure on the second server.
NOTE that you should ONLY use --initial if you are either starting from
scratch or have changed the config.ini file on the managment.
STAGE 4: Check its working
You can now return to the managment server (mysql3) and enter the managment console:
/usr/local/mysql/bin/ndb_mgm
Enter the command SHOW to see what is going on. A sample output looks like this:
[root@mysql3 mysql-cluster]# /usr/local/mysql/bin/ndb_mgm
-- NDB Cluster -- Management Client --
ndb_mgm>; show
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=2 @192.168.0.1 (Version: 4.1.9, Nodegroup: 0, Master)
id=3 @192.168.0.2 (Version: 4.1.9, Nodegroup: 0)
[ndb_mgmd(MGM)] 1 node(s)
id=1 @192.168.0.3 (Version: 4.1.9)
[mysqld(API)] 2 node(s)
id=4 (Version: 4.1.9)
id=5 (Version: 4.1.9)
ndb_mgm>;
If you see
not connected, accepting connect from 192.168.0.[1/2/3]
in the first or last two lines they you have a problem. Please email me
with as much detail as you can give and I can try to find out where you
have gone wrong and change this HOWTO to fix it.
If you are OK to here it is time to test mysql. On either server mysql1
or mysql2 enter the following commands: Note that we have no root
password yet.
mysql
use test;
CREATE TABLE ctest (i INT) ENGINE=NDBCLUSTER;
INSERT INTO ctest () VALUES (1);
SELECT * FROM ctest;
You should see 1 row returned (with the value 1).
If this works, now go to the other server and run the same SELECT and
see what you get. Insert from that host and go back to host 1 and see
if it works. If it works then congratulations.
The final test is to kill one server to see what happens. If you have
physical access to the machine simply unplug its network cable and see
if the other server keeps on going fine (try the SELECT query). If you
dont have physical access do the following:
ps aux | grep ndbd
You get an output like this:
root 5578 0.0 0.3 6220 1964 ? S 03:14 0:00 ndbd
root 5579 0.0 20.4 492072 102828 ? R 03:14 0:04 ndbd
root 23532 0.0 0.1 3680 684 pts/1 S 07:59 0:00 grep ndbd
In this case ignore the command "grep ndbd" (the last line) but kill
the first two processes by issuing the command kill -9 pid pid:
kill -9 5578 5579
Then try the select on the other server. While you are at it run a SHOW
command on the managment node to see that the server has died. To
restart it, just issue
ndbd
NOTE no --inital!
Further notes about setup
I strongly recommend that you read all of this (and bookmark this page). It will almost certainly save you a lot of searching.
The Managment Server
I strongly recommend that you do not stop the managment server once it has started. This is for several resons:
The server takes hardly any server resources
If a cluster falls over, you want to be able to just ssh in and type
ndbd to stat it. You dont want to have to start messing around with
another server
If you want to take backups then you need the managment server up
The cluster log is sent to the management server so to check what is
going on in the cluster or has happened since last this is an important
tool
All commands from the ndb_mgm client is sent to the management server
and thus no management commands without management server.
The managment server is required in case of cluster reconfiguration
(crashed server or network split). In the case that it is not running,
"split-brain" scenario will occure. The management server arbitration
role is required for this type of setup to provide better fault
tollerance.
However you are welcome to stop the server if you prefer.
Starting and stopping ndbd automatically on boot
To achieve this, do the following on both mysql1 and mysql2:
echo "ndbd" >; /etc/rc.d/init.d/ndbd
chmod +x /etc/rc.d/init.d/ndbd
chkconfig --add ndbd
Note that this is a really quick script. You ought really to write one
that at least checks if ndbd is already started on the machine.
Use of hostnames
You will note that I have used IP addresses exclusively throught this
setup. This is because using hostnames simply increases the number of
things that can go wrong. Mikael Ronstr
