Deploying Versions with Zero Downtime

To deploy with zero downtime

You can use the command line interface to deploy a new application with zero downtime. The following steps walk you through creating a configuration template, launching a new environment with the new application version using the configuration template, and swapping the environment CNAMEs. You can also use the following steps to perform configuration changes with zero downtime.

To deploy with zero downtime

An example script

#! /usr/bin/env ruby
require 'optparse'
require 'json'
require 'timeout'

options = {}
optparse = OptionParser.new do |opts|
opts.banner = "Usage: #{File.basename($0, ".rb")} [options] environment_id"

options[:verbose] = false
opts.on('-v', '--verbose', 'Output more information') do 
options[:verbose] = true;
end

options[:version_label] = nil
opts.on('-l LABEL', '--version-label', 'The application version to deploy to the new environment') do |label|
options[:version_label] = label
end

options[:application_name] = nil
opts.on('-a NAME', '--application-name', 'The name of the application associated with the version to deploy to the new environment.', 
      'Note if this is different from the application associated with the environment you are redeploying, the new environment will be associated with this application.') do |app|
options[:application_name] = app
end

opts.on('-h', '--help', 'Display this information') do 
puts opts
exit
end

end
optparse.parse!

verbose = options[:verbose]
puts "Verbose mode enabled" if verbose
environment_id = ARGV[0]
if (environment_id == nil)
puts optparse.to_s
exit
end

puts "Starting zero downtime deployment for environment: #{environment_id}" if verbose

## Verify Environment exists and has the right status
puts "Verifying environment exists and has correct status/health" if verbose

results = JSON.parse(%x[elastic-beanstalk-describe-environments -j -E #{environment_id}])
environment_info = results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'][0] if (results['DescribeEnvironmentsResponse'] &&
               results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult'] &&
               results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'])

if !environment_info
puts "No such environment found with environment_id: #{environment_id}"
exit
end

env_health = environment_info['Health']
env_status = environment_info['Status']
puts "Current Health: #{env_health}   Current Status: #{env_status}" if verbose
if (("Green" != env_health) || ("Ready" != env_status))
puts "Environment must be Ready and Green to perform a zero downtime deployment. Current Health: #{env_health}  Current Status: #{env_status}"
exit
end

## Verify version exists 
version_label = options[:version_label]
application_name = options[:application_name]

if (! application_name)
application_name = environment_info['ApplicationName']
end

if (! version_label)
version_label = environment_info['VersionLabel']
end

puts "Verifying version #{version_label} in application #{application_name} exists" if verbose
results = JSON.parse(%x[elastic-beanstalk-describe-application-versions -j -a #{application_name} -l #{version_label}])
version_info = results['DescribeApplicationVersionsResponse']['DescribeApplicationVersionsResult']['ApplicationVersions'][0] if (results['DescribeApplicationVersionsResponse'] &&
           results['DescribeApplicationVersionsResponse']['DescribeApplicationVersionsResult'] &&
           results['DescribeApplicationVersionsResponse']['DescribeApplicationVersionsResult']['ApplicationVersions'])

if (!version_info)
puts "No such version #{version_label} in application #{application_name} exists"
exit
end

environment_name = environment_info['EnvironmentName']

## New environment name will have 8 additional characters.  This is important since the environment
##  name is already limited to 25 characters in length (due to ELB usage).  
new_environment_name = environment_name.gsub(/_zdd_\d+$/, "_zdd_#{rand(10)}")

## Create a Configuration Template from the existing environment 
template_name = new_environment_name

puts "Creating ConfigurationTemplate named #{template_name}" if verbose
results = JSON.parse(%x[elastic-beanstalk-create-configuration-template -j -E #{environment_id} -a #{application_name} -t #{template_name}])
template_info = results['CreateConfigurationTemplateResponse']['CreateConfigurationTemplateResult'] if results['CreateConfigurationTemplateResponse']

if (! template_info)
puts "Error when creating configuration template: #{results}"
exit
end

## Launch a new environment with the desired version and template
puts "Creating new environment named #{new_environment_name}" if verbose
results = JSON.parse(%x[elastic-beanstalk-create-environment -j -a #{application_name} -l #{version_label} -e #{new_environment_name} -t #{template_name}} ])
new_environment_info = results['CreateEnvironmentResponse']['CreateEnvironmentResult'] if results['CreateEnvironmentResponse']

if (! new_environment_info)
puts "Error when launching new environment: #{results}"
exit
end

new_environment_id = new_environment_info['EnvironmentId']
puts "New environment: #{new_environment_info}" if verbose

## Wait for the new environment to go ready
## This wait can be customized for a given application to determine when it is really ready 

max_wait_time_sec = 5 * 60;  ## 5 minutes
begin
Timeout::timeout(max_wait_time_sec) do
done = false
while (! done) do 
  puts "Checking if new environment is ready/green" if verbose
  results = JSON.parse(%x[elastic-beanstalk-describe-environments -j -E #{new_environment_id}])
  new_environment_info = results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'][0] if (results['DescribeEnvironmentsResponse'] &&
                         results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult'] &&
                         results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'])

  puts "Current Health: #{new_environment_info['Health']}   Current Status: #{new_environment_info['Status']}" if verbose     
  done = (new_environment_info &&("Ready" == new_environment_info['Status']))
  if (! done)
    sleep 20  ## seconds
  end
end
end
rescue Timeout::Error
puts "Environment does not seem to be launching in a reasonable time.  Exiting after #{max_wait_time_sec} seconds"
exit
end

results = JSON.parse(%x[elastic-beanstalk-describe-environments -j -E #{new_environment_id}])
new_environment_info = results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'][0] if (results['DescribeEnvironmentsResponse'] &&
                   results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult'] &&
                   results['DescribeEnvironmentsResponse']['DescribeEnvironmentsResult']['Environments'])

if (! new_environment_info) 
puts "Error waiting for environment to launch: #{results}"
exit
end

if ("Green" != new_environment_info['Health'])
puts "New Environment is not healthy, aborting"
%x[elastic-beanstalk-terminate-environment -E #{new_environment_id}]
exit
end


## Execute CNAME swap
puts "Executing CNAME Swap between old environment #{environment_id} and new environment: #{new_environment_id}" if verbose
results = JSON.parse(%x[elastic-beanstalk-swap-environment-cnames j -S #{environment_id} -D #{new_environment_id}])

## Clean up resources

## Once comfortable that the environment swap has completed the old environment can be terminated
#results = JSON.parse(%x[elastic-beanstalk-terminate-environment -j -E #{environment_id}])

# Also delete the configuration template
#results = JSON.parse(%x[elastic-beanstalk-delete-configuration-template -j -a #{application_name} -t #{template_name}])

To deploy with zero downtime