Shantanu's Blog

Database Consultant

June 22, 2012


Create Auto-scaled load balancer

Create and configure load-balancer:
elb-create-lb MyLB --availability-zones us-east-1b --listener "protocol=TCP, lb-port=3306, instance-port=3306"

elb-configure-healthcheck MyLB --target "TCP:3306" --interval 30 --timeout 2 --healthy-threshold 6 --unhealthy-threshold 2

elb-register-instances-with-lb MyLB --instances i-29184c43

Create config parameter and auto-scaling group:
as-create-launch-config MyLC --image-id ami-41d00528 --instance-type m1.small --key severalnines --group quick-start-1 

as-create-auto-scaling-group MyAutoScalingGroup --launch-configuration MyLC --availability-zones us-east-1a  --min-size 2 --max-size 5 --load-balancers MyLB

Create policies and alarms:
as-put-scaling-policy MyScaleUpPolicy --auto-scaling-group MyAutoScalingGroup  --adjustment=1 --type ChangeInCapacity  --cooldown 300
mon-put-metric-alarm MyHighCPUAlarm  --comparison-operator  GreaterThanThreshold  --evaluation-periods  1 --metric-name  CPUUtilization  --namespace  "AWS/EC2"  --period  600  --statistic Average --threshold  80 --alarm-actions Policy_from_previous_step --dimensions "AutoScalingGroupName=MyAutoScalingGroup"

as-put-scaling-policy MyScaleDownPolicy --auto-scaling-group MyAutoScalingGroup  --adjustment=-1 --type ChangeInCapacity  --cooldown 300

mon-put-metric-alarm MyLowCPUAlarm  --comparison-operator  LessThanThreshold --evaluation-periods  1 --metric-name  CPUUtilization --namespace  "AWS/EC2"  --period  600  --statistic Average --threshold 40 --alarm-actions Policy_from_previous_step --dimensions "AutoScalingGroupName=MyAutoScalingGroup"

Describe scaling: 


associate domain:
## associate and dis-associate route 53 domain to LB
elb-associate-route53-hosted-zone useast --rr-name --hosted-zone-id Z36XR238KZYP2F --weight 100

elb-disassociate-route53-hosted-zone useast --rr-name --hosted-zone-id Z36XR238KZYP2F --weight 100

Pause auto-scale:

as-suspend-processes MyAutoScalingGroup
as-resume-processes  MyAutoScalingGroup

Delete config parameter and auto scale group:
as-delete-auto-scaling-group MyAutoScalingGroup  --force-delete

as-delete-launch-config  MyLC

Replace launch config:

as-create-launch-config app-server-launch-config-2 --image-id ami-c503e8ac --instance-type c1.medium --group web

as-update-auto-scaling-group app-server-as-group-1 --launch-configuration app-server-launch-config-2

Terminate instances:
as-update-auto-scaling-group app-server-as-group-1 --min-size 0

as-terminate-instance-in-auto-scaling-group i-12345abc --decrement-desired-capacity

as-terminate-instance-in-auto-scaling-group i-12345abc --no-decrement-desired-capacity


June 18, 2012


Script to install mysql

Here is the shell script that will install mysql version 5.5 on a new instance.
sh -xv /root/


# mysql data directory

mydate=`date '+%j%H%M%S'`

## make sure new EBS is formatted
#time mkfs /dev/xvdt

## Add mount point if any and mysql start command in /etc/rc.local

#/bin/mkdir -p /data
#/bin/mount /dev/xvdab /data
#/etc/init.d/iptables stop
#/etc/init.d/mysql start

## disable selinux
sed -i 's/SELINUX=enforcing/SELINUX=disabled/' /etc/sysconfig/selinux
/usr/sbin/setenforce 0
echo 0 > /selinux/enforce

## shut-down mysql if already running
mysqladmin shutdown

# remove old data directory
#rm -rf /var/lib/mysql/
rm -rf /root/download

## create required directories
# datadir
mkdir -p $my_data_dir
# pid directory
mkdir -p /var/run/mysql
# default socket directory
mkdir -p /var/lib/mysql
# download directory
mkdir /root/download
cd /root/download


# create my.cnf file
cat > /etc/my.cnf << heredoc




## logging


## date %j%H%M%Sserver-id=$mydate

## network and slave needs more bandwidth

## temporary tables optimization

## join queries use this buffer

## Query Cache
query_cache_type = 1
query_cache_size = 200M

## Performance Tunning

## temp dir
tmpdir = /mnt/

## InnoDB optimization

mysqld = /usr/bin/mysqld_safe
mysqladmin = /usr/bin/mysqladmin
user = multi_admin
password = multipass

socket = /tmp/mysql.sock2
port = 3307
pid-file = /mnt/data/hostname.pid2
datadir = /mnt/data/



# reset data-directory
mydir=`grep ^datadir /etc/my.cnf | awk -F'=' '{print $2}'`
rm -rf $mydir/*

# remove mysql
for package in `rpm -qa | grep -i mysql`
rpm -e $package

rpm -e mysql-libs-5.1.52-1.el6_0.1.x86_64

# install mysql
rpm -iUh /root/download/*

# install php
yum install -y php

# install mysql system files
mysql_install_db --datadir=$mydir

# restart mysql
/etc/init.d/mysql restart

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June 15, 2012


Using Auto Scaling with load-balancer

We can increase / decrease instances based on a particular image that will have all the data built-in. Here are the 4 commands those we can execute to create the auto-scaling group. Auto Scaling and Load Balancing tools can be installed from the following links...

Load balancer can be easily created / disabled from the web interface. But I guess for auto-scaling we will need to install the command line tool mentioned above.

1) Create a load balancer:
elb-create-lb mysql_LoadBal --listener "1b-port=3306,instance-port=3306,protocol=TCP" --availability-zones us-east-1b

2) Create auto scaling group launch configuration:
as-create-launch-config mysql_Config --image-id ami-60da3d09 --instance-type m1.small

3) Create auto scaling group:
as-create-auto-scaling-group mysql_AutoScale --launch-configuration mysql_Config --availability-zones us-east-1b --min-size 1 --max-size 5 load-balancers mysql_LoadBal

4) Create Trigger:
as-create-or-update-trigger mysql_Trigger1 --auto-scaling-group mysql_AutoScale --namespace "AWS/EC2" --measure CPUUtilization --statistic Average --dimensions "AutoScalingGroupName=mysql_AutoScale" --units "Percent" --period 60 --lower-threshold 30 --upper-threshold 70 --lower-breach-increment"=-1" --upper-breach-increment "1" --breach-duration 120

When average CPU utilization in the group exceeds 70% over a two-minute interval, increase instances up-to maximum of 5. When load falls below 30% reduce the number of instances but keep at-least 1 instance running.

To check how it is working:
as-describe-scaling-activities mysql_AutoScale

i) In order to disable auto-scaling We will first have to remove the trigger:
as-delete-trigger mysql_Trigger1 --auto-scaling-group mysql_AutoScale

ii) Set minimum and maximum size of the group to 0 to force all its instances to terminate:
as-update-auto-scaling-group mysql_AutoScale --min-size 0 --max-size 0

iii) Remove auto-scaling group:
as-delete-auto-scaling-group mysql_AutoScale

iV) Remove load balancer:
elb-delete-lb mysql_LoadBal



EC2 Instance Metadata

Each EC2 instance can access run-time data about itself by making HTTP requests to the special address

wget -q

cat instance-id

You can also supply your own metadata when you launch an EC2 instance. This data is called "User Data". For e.g.

wget -q
cat user-data

You can have your custom AMI treat the user metadata as the URL of the script to be run when the instance starts.



EBS Raid

We can glue the EBS volumes together into a RAID.

mdadm --create /dev/md0 --level 0 --metadata=1.1 --raid-devices 2 /dev/sdh1 /dev/sdh2

Add the following line to /etc/mdadm.conf (creating if necessary)

DEVICES /dev/sdh1 /dev/sdh2

Run the following command to add additional configuration information to the file:

mdadm --detail --scan >> /etc/mdadm.conf

At this point the RAID volume (/dev/md0) has been created. It encapsulates the 2 volumes.

Create a file system:

mkfs /dev/md0

create a mount point and mount the volume on it:

mkdir /data
mount /dev/md0 /data


June 12, 2012


Check return code

While using "system" function to execute linux commands within PHP, we can use a variable to store the return value. We will continue only if the return value is 0 (success) or exit the script.

system("mysqldump -uroot db1 --ignore-table=db1.tbl_1 --ignore-table=db1.tbl_2 > /root/db1.sql", $retval);

if ($retval != '0') {
  exit ("dump db1.sql command failed");

June 08, 2012


Restarting slave

I have always ignored the following warning.

[Warning] Neither --relay-log nor --relay-log-index were used; so replication may break when this MySQL server acts as a slave and has his hostname changed!! Please use '--relay-log=slave-usw-relay-bin' to avoid this problem.

This made a big difference when I changed the AWS EBS and attached it to a new instance. Since the new instance had a new IP address, the relay-log file name was inconsistent. Therefore we must always specify log-bin and relay-log parameters in my.cnf


It is possible to recover slave if it has Failed to open the relay log. It is possible that MySQL saved it's relay logs in /var/run by default, which gets cleared out on boot.

To fix this, there are 2 ways.

you need to change the location MySQL uses for the logging by adding the following line to the [mysqld] section of /etc/my.cnf

relay-log = /var/lib/mysql/relay-bin

Then edit /var/lib/mysql/ to point to the first new relay log (leaving the master information the same.


Start the slave. Or if you already have the slave status at the time of stopping the slave. Note the following 2 parameters.

       Relay_Master_Log_File: mis-bin.000710
          Exec_Master_Log_Pos: 461352141

And then reset slave and start the replication by using the statement "CHANGE MASTER TO ..."


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