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Colin Johnson 2012-08-31 07:12:37 +00:00
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# Introduction:
aws-ha-release.sh is created to allow the automated and no downtime replacement of all EC2 Instances in an Auto Scaling Group that is behind an Elastic Load Balancer.
#
# Potential Use:
Some potential uses aws-ha-release.sh are listed below:
1. Delivery of new code - if your deployment scheme utilizes the "cycling" or "rolling" of EC2 instances to bring new code into production, aws-ha-release.sh provides an automated way to do this without incurring any downtime
2. Return of all EC2 instances to "pristine" or "vanilla" state - all older EC2 instances can be replaced with newer EC2 instances
# Directions For Use:
#
## Example of Use:
#
aws-ha-release.sh -a my-scaling-group
-
the above example would terminate and replace each EC2 Instance in the Auto Scaling group "my-scaling-group" with a new EC2 Instance.
#
## Required Options:
#
aws-ha-release.sh requires the following option:
-a <auto-scaling-group-name> - the name of the Auto Scaling Group for which you wish to perform a no downtime
#
## Optional Parameters:
#
-r <region> - allows you specify the region in which your Auto Scaling Group and Launch Configuration are in. By default aws-ha-release.sh assumes the "us-east-1" region.
-t <elb_timeout> - time, in seconds, in which an EC2 instance should be given to complete request processing prior to being terminated. Set this value high enough so that any requests sent through an ELB would have time to be completed by an EC2 instance. For example: if the ELB allows connections to stay open for 120 seconds then setting this value to 120 seconds allows an instance behind an ELB 120 seconds to complete all processing before being terminated. By default both an AWS ELB and aws-ha-release.sh utilize 60 seconds timeout period.
-i <inservice_time_allowed> - allows you to specify the number of seconds an EC2 instance is provided to come into service. By default EC2 instances are given 300 seconds to come into service - if aws-ha-release.sh notices that an instance has not come into service in 300 seconds it will exit and return an exit status of 79. If an EC2 instance and application combination requires more than 300 seconds to come "InService" from the perspective of an ELB then this value should be set to a greater number.
#
# Additional Information:
#
Author: Colin Johnson / colin@cloudavail.com
Date: 2012-08-31
Version 0.1
License Type: GNU GENERAL PUBLIC LICENSE, Version 3

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#!/bin/bash -
# Author: Colin Johnson / colin@cloudavail.com
# Date: 2012-08-11
# Version 0.1
# License Type: GNU GENERAL PUBLIC LICENSE, Version 3
#
#####
#confirms that executables required for succesful script execution are available
prerequisitecheck()
{
for prerequisite in basename grep cut as-describe-auto-scaling-groups as-update-auto-scaling-group elb-deregister-instances-from-lb as-terminate-instance-in-auto-scaling-group elb-describe-instance-health
do
#use of "hash" chosen as it is a shell builtin and will add programs to hash table, possibly speeding execution. Use of type also considered - open to suggestions.
hash $prerequisite &> /dev/null
if [[ $? == 1 ]] #has exits with exit status of 70, executable was not found
then echo "In order to use $app_name, the executable \"$prerequisite\" must be installed." 1>&2 ; exit 70
fi
done
}
return_as_initial_maxsize()
{
if [[ $max_size_change -eq 1 ]]
then echo "$asg_group_name had its max-size increased temporarily by 1 to a max-size of $asg_temporary_max_size. $app_name will now return the max-size of $asg_group_name to its original max-size of $asg_initial_max_size."
#decrease max-size by 1
as-update-auto-scaling-group $asg_group_name --region $region --max-size=$asg_initial_max_size
fi
}
return_as_initial_desiredcapacity()
{
echo "$asg_group_name had its desired-capacity increased temporarily by 1 to a desired-capacity of $asg_temporary_desired_capacity. $app_name will now return the desired-capacity of $asg_group_name to its original desired-capacity of $asg_initial_desired_capacity."
as-update-auto-scaling-group $asg_group_name --region $region --desired-capacity=$asg_initial_desired_capacity
}
#set application defaults
app_name=`basename $0`
elb_timeout=60
region="us-east-1"
#max_size_change is used as a "flag" to determine if the max-size of an Auto Scaling Group was changed
max_size_change="0"
inservice_time_allowed=300
inservice_polling_time=10
delimiter="%"
#calls prerequisitecheck function to ensure that all executables required for script execution are available
prerequisitecheck
#handles options processing
while getopts :a:t:r:i: opt
do
case $opt in
a) asg_group_name="$OPTARG";;
t) elb_timeout="$OPTARG";;
r) region="$OPTARG";;
i) inservice_time_allowed="$OPTARG";;
*) echo "Error with Options Input. Cause of failure is most likely that an unsupported parameter was passed or a parameter was passed without a corresponding option." 1>&2 ; exit 64 ;;
esac
done
#validate elb_timeout is number
##code to be written
if [[ -z $asg_group_name ]]
then echo "You did not specify an Auto Scaling Group name. In order to use $app_name you must specify an Auto Scaling Group name using -a <autoscalingroupname>." 1>&2 ; exit 64
fi
#region validator
case $region in
us-east-1|us-west-2|us-west-1|eu-west-1|ap-southeast-1|ap-northeast-1|sa-east-1) ;;
*) echo "The \"$region\" region does not exist. You must specify a valid region (example: -r us-east-1 or -r us-west-2)." 1>&2 ; exit 64;;
esac
#creates variable containing Auto Scaling Group
asg_result=`as-describe-auto-scaling-groups $asg_group_name --show-long --max-records 1000 --region $region --delimiter $delimiter`
#validate Auto Scaling Group Exists
#user response for Auto Scaling Group lookup - alerts user if Auto Scaling Group was not found.
if [[ $asg_result = "No AutoScalingGroups found" ]]
then echo "The Auto Scaling Group named \"$asg_group_name\" does not exist. You must specify an Auto Scaling Group that exists." 1>&2 ; exit 64
fi
#validate - the pipeline of echo -e "$aasg_result" | grep -c "AUTO-SCALING-GROUP" must only return one group found - in the case below - more than one group has been found
if [[ `echo -e "$asg_result" | grep -c "^AUTO-SCALING-GROUP"` > 1 ]]
then echo "More than one Auto Scaling Group found. As more than one Auto Scaling Group has been found, $app_name does not know which Auto Scaling Group should have Instances terminated." 1>&2 ; exit 64
fi
#validate - the pipeline of echo -e "$asg_result" | grep -c "AUTO-SCALING-GROUP" must only return one group found
if [[ `echo -e "$asg_result" | grep -c "^AUTO-SCALING-GROUP"` < 1 ]]
then echo "No Auto Scaling Group was found. Because no Auto Scaling Group has been found, $app_name does not know which Auto Scaling Group should have Instances terminated." 1>&2 ; exit 64
fi
#gets Auto Scaling Group max-size
asg_initial_max_size=`echo $asg_result | grep ^AUTO-SCALING-GROUP | cut -d "$delimiter" -f 10`
asg_temporary_max_size=$(($asg_initial_max_size+1))
#gets Auto Scaling Group desired-capacity
asg_initial_desired_capacity=`echo "$asg_result" | grep ^AUTO-SCALING-GROUP | cut -d "$delimiter" -f 10`
asg_temporary_desired_capacity=$((asg_initial_desired_capacity+1))
#gets list of Auto Scaling Group Instances - these Instances will be terminated
asg_instance_list=`echo "$asg_result" | grep ^INSTANCE | cut -d "$delimiter" -f 2`
asg_elb=`echo "$asg_result" | grep ^AUTO-SCALING-GROUP | cut -d "$delimiter" -f 6`
#if the max-size of the Auto Scaling Group is zero there is no reason to run
if [[ $asg_initial_max_size -eq 0 ]]
then echo "$asg_group_name has a max-size of 0. As the Auto Scaling Group \"$asg_group_name\" has no active Instances there is no reason to run." ; exit 79
fi
#echo a list of Instances that are slated for termination
echo -e "The list of Instances in Auto Scaling Group $asg_group_name that will be terminated is below:\n$asg_instance_list"
#if the desired-capacity of an Auto Scaling Group group is greater than or equal to the max-size of an Auto Scaling Group, the max-size must be increased by 1 to cycle instances while maintaining desired-capacity. This is particularly true of groups of 1 instance (where we'd be removing all instances if we cycled).
if [[ $asg_initial_desired_capacity -ge $asg_initial_max_size ]]
then echo "$asg_group_name has a max-size of $asg_initial_max_size. In order to recycle instances max-size will be temporarily increased by 1 to max-size $asg_temporary_max_size."
#increase max-size by 1
as-update-auto-scaling-group $asg_group_name --region $region --max-size=$asg_temporary_max_size
#sets the flag that max-size has been changed
max_size_change="1"
fi
#increase groups desired capacity to allow for instance recycling without decreasing available instances below initial capacity
echo "$asg_group_name is currently at $asg_initial_desired_capacity desired-capacity. $app_name will increase desired-capacity by 1 to desired-capacity $asg_temporary_desired_capacity."
as-update-auto-scaling-group $asg_group_name --region $region --desired-capacity=$asg_temporary_desired_capacity
#and begin recycling instances
for instance_selected in $asg_instance_list
do
#the while loop below sleeps for the auto scaling group to have an InService capacity that is equal to the desired-capacity + 1
while [[ $inservice_instance_count -lt $asg_temporary_desired_capacity ]]
do
if [[ $inservice_time_taken -gt $inservice_time_allowed ]]
then echo "During the last $inservice_time_allowed seconds the InService capacity of the $asg_group_name Auto Scaling Group did not meet the Auto Scaling Group's desired capacity of $asg_temporary_desired_capacity." 1>&2
#return max-size to initial size
return_as_initial_maxsize
#return temporary desired-capacity to initial desired-capacity
return_as_initial_desiredcapacity
exit 79
fi
inservice_instance_list=`elb-describe-instance-health $asg_elb --region $region --show-long | grep InService`
inservice_instance_count=`echo "$inservice_instance_list" | wc -l`
#sleeps a particular amount of time
sleep $inservice_polling_time
inservice_time_taken=$(($inservice_time_taken+$inservice_polling_time))
echo $inservice_instance_count "Instances are InService status. $asg_temporary_desired_capacity Instances are required to terminate the next instance. $inservice_time_taken seconds have elapsed while waiting for an Instance to reach InService status."
#if any status in $elbinstsancehealth != "InService" repeat
done
#if the
echo "$asg_group_name has reached a desired-capacity of $asg_temporary_desired_capacity. $app_name can now remove an Instance from service."
inservice_instance_count=0
inservice_time_taken=0
#remove instance from ELB - this ensures no traffic will be directed at an instance that will be terminated
echo "Instance $instance_selected will now be deregistered from ELB \"$asg_elb.\""
elb-deregister-instances-from-lb $asg_elb --region $region --instances $instance_selected > /dev/null
#sleep for "elb_timeout" seconds so that the instance can complete all processing before being terminated
sleep $elb_timeout
#terminates a pre-existing instance within the autoscaling group
echo "Instance $instance_selected will now be terminated. By terminating this Instance, the actual capacity will be decreased to 1 under desired-capacity."
as-terminate-instance-in-auto-scaling-group --instance $instance_selected --no-decrement-desired-capacity --force > /dev/null
done
#return max-size to initial size
return_as_initial_maxsize
#return temporary desired-capacity to initial desired-capacity
return_as_initial_desiredcapacity