Cloudformation - Redeploy environment that uses a recordset (with Jenkins) - amazon-web-services

Question

TL;DR - What's the recommended way, using a CI server, to keep an AWS environment up to date, and always pointed to from the same CNAME?
We're just starting to use AWS with a new project, and as part of the project I've been tasked with creating a simple demo environment, and updating this environment each night to show the previous days progress.
I'm using Jenkins and the Cloudformation plugin to do this, and it works great in creating a simple EC2 instance in an existing security group, pointed to by a Route53 CNAME so it can be browsed at subdomain.example.com.
The problem I have is that I can't redeploy the same stack, because the recordset already exists, and CF won't overwrite it.
There are lots of guides on how to deploy an environment, but I'm struggling to find one on how to keep an environment up to date.
So I guess my question is: What's the recommended way, using a CI server, to keep an AWS environment up to date, and always pointed to from the same CNAME?

Answer 1

I agree with the comments in your question i.e. probably better to create a clean server and upload / update to it via continuous integration (Jenkins). Docker is super useful in this scenario which you mentioned in a later comment.
However, if you are leaning towards "immutable infrastructure" and want everything encapsulated in your CloudFormation template (Including creating a record in Route53) you could do something like the following code snippet in your AWS::CloudFormation::Init section - (See 'http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource- init.html' for more info)
"Resources": {
"MyServer": {
"Type": "AWS::EC2::Instance",
"Metadata": {
"AWS::CloudFormation::Init": {
"configSets" : { "Install" : [ "UpdateRoute53", "ConfigSet2, .... ] },
"UpdateRoute53" : {
"files" : {
"/usr/local/bin/cli53" : {
"source" : "https://github.com/barnybug/cli53/releases/download/0.6.3/cli53-linux-amd64",
"mode" : "000755", "owner" : "root", "group" : "root"
},
"/tmp/update_route53.sh" : {
"content" : { "Fn::Join" : ["", [
"#!/bin/bash\n\n",
"PRIVATE_IP=`curl http://169.254.169.254/latest/meta-data/local-ipv4/`\n",
"/usr/local/bin/cli53 rrcreate ",
{"Ref": "Route53HostedZone" },
" \"", { "Ref" : "ServerName" },
" 300 A $PRIVATE_IP\" --replace\n"
]]},
"mode" : "000755", "owner" : "root", "group" : "root"
}
},
"commands" : {
"01_UpdateRoute53" : {
"command" : "/tmp/update_route53.sh > /tmp/update-route53.log 2>&1"
}
}
}
}
},
"Properties": { ... }
}
}
....
I've ommitted large chunks of the template to focus on the important info. The "UpdateRoute53" section creates 2 files:
/usr/local/bin/cli53 - CLI53 is a great little wrapper program around AWS Route53 (as AWS CLI version of route53 is pretty horrible to use i.e. requires creating large chunks of JSON) - see https://github.com/barnybug/cli53 for more info on CLI53
/tmp/update_route53.sh - creates a script to upload to Route53 via the CLI53 script we installed in (1). This script determines the PRIVATE_IP via a curl comand to the special AWS meta data endpoint (see http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html for more details). The "zone id" to the correct hosted zone is injected via a CloudFormation parameter (i.e. {"Ref": "Route53HostedZone" }). Finally the name of the record comes from the "ServerName" parameter but how this is set could vary from template to template.
In the "commands" section we run the script we created in "files" section (2) and output the results a log file in the /tmp folder.
NOTE (1) - The parameter Route53HostedZone can be declared as follows: -
"Route53HostedZone": {
"Description": "Route 53 hosted zone for updating internal DNS",
"Type": "AWS::Route53::HostedZone::Id",
"Default": "VIWIWK4PYAC23B"
}
The cool thing about the "AWS::Route53::HostedZone::Id") parameter type is that it displays a combo box (when running a CloudFormation template via the AWS web console) showing the zone name with the value being the Zone ID.
NOTE (2) - The --replace attribute in the CLI53 script overrides existing records which is probably what you want.
NOTE (3) - Another option would be to SSH via Jenkins (e.g. using the the "Publish Over SSH Plugin" - https://wiki.jenkins-ci.org/display/JENKINS/Publish+Over+SSH+Plugin), determine the private IP and using the CLI53 script update Route53 either from the server you've logged into or even the build server (when Jenkins is running).
Lots of options - hope you get it sorted! :-)