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cfnassit is to a tool help with cloud formation deployments into AWS VPCs

Current Release

Current Version 1.2.85

Dependencies refresh release.

Previous Releases

Version 1.1.37

Build Status


Key Features

  • Works with the existing syntax of cloud formation json, it just uses some simple conventions for parameters
  • Implements a simple Project/Environment abstraction on top of AWS VPCs (i.e. cfnassit/qa or cfnassit/dev)
  • Manages application of create and update cloudformation scripts against particular Projects and Environments
  • Tracks which scripts need to be applied to projects and environments using a simple delta tracking mechanism borrowed from dbdeploy
  • Autopopulates physical id's based on logical identifiers plus the project & environment, this means you can break large scripts apart and think about project/env/logical ids instead of VPC id/physical id
  • Assists with the Phoenix Server pattern by automating the switch over of instances for an ELB based on build numbers
  • Allows upload to S3; along with the option of passing S3 urls of new aritifacts directly into cloudformation templates
  • Use VPC Tags as input or output to templates using a simple convention in the parameter description
  • Automatically pick up values from environmental variables and availability zones to use in template parameters
  • Generates diagrams of VPCs by producing graphviz format files
  • Manage ELB security groups by allowing you to add/remove your current IP to/from a specified environment
  • Send notifcations via SNS for stack CREATE or DELETE actions


The tool provides a command line interface and ant tasks. Examples of the CLI use below, see exampleAntTasks.xml for ant task usage.


Creating AWS resources can mean you might be liable for charges. Please check the AWS documentation.


You need to be familiar with AWS, in particular VPCs and Cloud Formation.


  • The tool uses DefaultAWSCredentialsProviderChain to connect to AWS, please read to understand how to authenticate with cfnassist.
  • The tool uses DefaultAWSCredentialsProviderChain to determine the region to operate in.
  • For certain key parameters the tool checks for environmental variables, for example CFN_ASSIST_PROJECT and CFN_ASSIST_ENV, this is useful if you use tools like autoenv or are working on a particular project a lot.

Documentation TODOs

  • Mention rate limits and the caching approach?
  • Add links to the various example json files in the test/cfnScripts folder


The example CLIs below assume you have the environmental variable CFN_ASSIST_PROJECT set to your project, that cfnassist is on the PATH and the credentials and regions are available via the default AWS mechanisms, see notes above.

export PATH=${PATH}:somepath/cfnassit-1.0.85/bin

1.Create a VPC and initialise with a Project and Environment

First create a VPC, for example:

aws ec2 create-vpc --cidr-block


VPC dopt-5e4f5b3c default pending vpc-926e8bf7

Wait for the create to finish, use this to check the status

aws ec2 describe-vpcs


VPCS dopt-5e4f5b3c default False available vpc-926e8bf7

Now use cfnassit to init the vpc with the tags it uses to id vpc's and track changes.

cfnassist -env Dev -init vpc-926e8bf7

Replace vpc-926e8bf7 with the ID of your VPC.

Check this work as expected using

aws ec2 describe-vpcs

You should see the VPC now has three tags associated with it:

VPCS dopt-5e4f5b3c default False available vpc-926e8bf7

Repeat above steps for other envs such as UAT and Prod

2.Set up your infrastructure

This typically includes the things you don't need to change on every release. For example subnets, load balancers, NAT and internet gateways and so on. You may still want to clean out a VPC and rerun this on occasions to make sure you can fully recreate a fully working VPC from scratch. Live instances etc should probably be created during the CI build especially if you are doing blue/green deploys. More on this below.

After each script succeeds the VPC CFN_ASSIST_DELTA tag is updated, this way the tool only tries to create the required stacks for each VPC. The tool will also take care of deleting an existing stack if it is in the rollback complete state.

cfnassist -env Dev -dir ./infrastructure

My infrastructure dir looks like this:

-rw-r--r-- 1 icartwri staff 1748 13 Jan 15:30 001subnets.json
-rw-r--r-- 1 icartwri staff 510 13 Jan 15:26 002internetGateway.json
-rw-r--r-- 1 icartwri staff 6287 13 Jan 21:34 003webSubnetAclAndSG.json
-rw-r--r-- 1 icartwri staff 1521 13 Jan 21:41 004dbSubnetAclAndSG.json
-rw-r--r-- 1 icartwri staff 5672 13 Jan 21:35 005intSubnetAclAndSG.json
-rw-r--r-- 1 icartwri staff 6572 9 Apr 15:46 006monSubnetAclAndSG.json
-rw-r--r-- 1 icartwri staff 5818 13 Jan 15:26 007natSubnetAclAndSG.json
-rw-r--r-- 1 icartwri staff 2842 13 Jan 21:46 008lbSubnetACLandSG.json
-rw-r--r-- 1 icartwri staff 1406 13 Jan 21:30 009natServer.json
-rw-r--r-- 1 icartwri staff 875 13 Jan 21:30 010elasticLoadBalancer.json
-rw-r--r-- 1 icartwri staff 3895 13 Jan 21:31 011routing.json

The tool executes these in numeric order, hence the filenames beginning with numbers, it does 'create' by default but can also do 'updates', see below.

Use Logical IDs

The tool will inject the correct Physical ID for a resource based on the current VPC, it finds the correct VPC using the Project and Environment . You can declare a parameter exactly as normal for cloudformation but follow the convention below and cfn assit will find the correct physical ID:

"Parameters" : {
"env" : { "Type" : "String" },
"vpc" : { "Type" : "String" },
"natSubnet" : { "Type" : "String" , "Description" : "::natSubnet" }

In this example ::natSubnet triggers to cfn assist find the right Physical ID for that logical ID in the current VPC, it does this by scanning the stacks associated with the current VPC for that logical ID. Also note the tool automatically injects the correct VPC and env (i.e. dev, UAT, Prod, etc).

So the example above will apply all the cfn scripts found in the infrastructure dir in order, the cloud formation stacks created will include the project and env in their name as well as the filename. There are also tagged with the project and env (and build number if present, more on that below....)


If all goes will the VPC tags get updated with the new delta index, so for example:


You should also be able to see all the associated stacks using

aws cloudformation describe-stacks

Create or Update?

By default cfnassit invokes cloud formation 'create', but if the filename contains ends with .update.json (or .delta.json) it will do a cloud formation 'update' instead. As described above cfnassit will keep track of which creates and updates been applied. The semantics of cloud formation updates are complex and specific to the resource type involved, you need to check the AWS documents especially as some updates can actually result in a resource being recreated.

3.Rolling changes back

Use with CARE!

This first command will rollback all delta's by deleting the stacks for a VPC in the correct order and updating the DELTA tag on the VPC as it goes! You may want to do this while getting things bedded in initially or when you want to check you can fully recreate an environment.

cfnassist -env Dev -purge

cfnassist -env Dev -rollback ./infrastructure is now deprecated, please use -purge which will work if your stack was create after version 1.0.25.

Alternatively you can roll back just the last change using:

cfnassist -env Dev -stepback

cfnassist -env Dev -back ./infrastructure is now deprecated, please use -back which will work if your stack was create after version 1.0.25.

4.Built-in parameters and Mappings

cnfassit auto-populates some parameters when it invokes the cloud formation api, you need to make sure these parameters are declared in your json otherwise the api will throw an error. The pre-populated variables are env and vpc, so you need to declare them:


You can then use cloudformation mappings in the usual way to inject environment specific parameters i.e.

"Mappings" : {
"environMap" : {
"qa" : { "keyName" : "techLab", "NatEip" : "eipalloc-0fb76661" },
"test" : { "keyName" : "techLab", "NatEip" : "TBA" },
"prod" : { "keyName" : "techLab", "NatEip" : "eipalloc-1de56375" }

The automatically populated env parameter is a more portable way to do this than mappings based on the VPC ID, especially if you need to recreate an environment/vpc from scratch or move to a different AWS region.

Use the mappings exactly as normal in cloudformation:

"KeyName": { "Fn::FindInMap" : [ "environMap", { "Ref" : "env" }, "keyName" ]} ,

5.Create instances (without build numbers)

For some longer lived services/instances you can include them in your 'infrastructure' delta directory, but sometimes it is more flexible to create them seperately.

For example RDS instances might be a resource you create but don't want to create/delete on each build.

cfnassist -env Dev -file ./rdsInstance.json

NOTE: If you are now getting InsufficientCapabilitiesException or MissingCapabilities exceptions

Amazon made a change to the API, for some types of resources you will get the above exceptions. To avoid this capabilities must be set on the create call. Use -capabilityIAM on the CLI or add capabilityIAM="true" to the cfnassist ant task. There is an example in distribution file exampleAntTasks.xml.

6.Create instances with build numbers

This is probably the more normal way to create instances, for example if you are using the Phoenix Server pattern.

cfnassist -env Dev -file ./rdsInstance.json -build 876

This will create a stack, with the stack and the instances tagged additionally with CFN_ASSIST_BUILD_NUMBER, the stack name will also include the build number.

7.List out the stacks

Work in progress: display format, not having to give the project, plus list out managed VPCs

You can list out the stacks cfnassit is managing for a particular project/env using

cfnassist -env Dev -ls

8.Pass parameters into the cloud formation scripts

You can declare the parameters exactly as you would for cloud formation. You can then pass values into them using the parameters argument.

cfnassist -env Dev -file ./rdsInstance.json -build 876 -parameters "testA=123;testB=123"

Note: You'll need to escape the ; character as appropriate for your shell/cli

9.Switch over ELB instances using Build Number

This lets you switch over the instances an ELB is pointing at based on build number and a special tag CFN_ASSIST_TYPE.

You need to set this type tag on the instances yourself, for example including the following in your instance definition:

"Tags": [
{ "Key" : "Name", "Value": "aTestInstance" },
{ "Key" : "CFN_ASSIST_TYPE", "Value": "web" }

Now you can switch over the ELB using

cfnassist -env Dev -build 876 -elbUpdate web

This will find all the instances created in cloud formation stacks for the project/env and that have the appropriate CFN_ASSIST_TYPE tag.

Next cfnassist finds the ELB for the VPC for the project and environment, addes the instances it found above to the ELB and removes any instances not matching the build number from the ELB.

You can 'rollback' the ELB to point at the previous instances by giving their build number, so you may not want to immediately delete previous instances until sure all is ok with the new ones.

If more than one ELB is found then cfnassist will check if the tag CFN_ASSIST_TYPE is present and matches the type tag you give above, if it is the tool will use that ELB, otherwise an error will be thrown.

10.Reset the delta tag on a VPC

Use with CARE!

This will reset the delta index tag on the corresponding VPC back to 0.

cfnassist -env Dev -reset

If you have cloud formation stacks associated with the VPC you will not be able to manage them using cfnassit if you do this.

11.Using SNS instead of polling for stack monitoring

By default cfnassist uses polling to check the status of stacks being created/updated/deleted. Cloud formation has the ability to publish SNS notifications as the status of a stack changes, and cfn assit can use these instead of polling to track status.

This avoids using polling meaning less network traffic and less chance of hitting 'rate limits' on the API

If you specify -sns on the commandline then cfnassit will

  1. Create a SNS topic using the name CFN_ASSIST_EVENTS (if it does not exist already)
  2. Create a SQS queue using the name CFN_ASSIST_EVENT_QUEUE (again, only if required)
  3. Create a policy meaning that SNS can publish the notifications to the queue. (and again, only if requied)
  4. Finally it will subscribe the Queue to the SNS notifications.

If you try to delete a stack using the SNS option when the stack was not originally created with the flag set this will fail, however stack updates will work as expected.

12.Upload files or folders to S3 and inject corresponding URLs into templates

You can use cfnassist to upload files or folders into S3 and then pass in the S3 url's of those files into templates automatically. The files will be prefixed with the build number i.e. /BUILDNUMBER/filename

The path to the file will be replaced with the URL, for example

cfnassist -env Dev -file templateFile.json -artifacts "urlA=dist/release.txt;urlB=dist/deployable.tgz" -bucket bucketName MyBucket -build 1123

This will upload the files release.txt and deployable.tgz to S3 bucket MyBucket and then populate the parameters urlA and urlB with the corresponding S3 urls and pass these into templateFile.json.

You can also upload the contents of a folder, in this case the path to the folder will be replaced with the URL of the bucket and key.

NOTE The current file path is not used, so the file dist/release.txt will end up in the bucket MyBucket with the key 1123/release.txt, this applies to the individual files within a folder also.

You can use the environmental variable CFN_ASSIST_BUCKET to specify the S3 bucket to use.

13.Upload or delete arifacts in S3

Sometimes you want to create or delete things in S3 independently of deploying templates.

cfnassist -env Dev -s3create -artifacts "xzy=dist/release.txt;abc=dist/deployable.tgz" -bucket bucketName MyBucket -build 1123


cfnassist -env Dev -s3create -artifacts "folder=dist/subFolder" -bucket bucketName MyBucket -build 1123

The files will be uploaded as per 12 above.

To delete files you need to need to pass in the name of the files themselves.

cfnassist -env Dev -s3delete -artifacts "mno=release.txt;rst=deployable.tgz -bucket bucketName MyBucket -build 1123

NOTE The current file path is not used, so the file dist/release.txt will end up in the bucket MyBucket with the key 1123/release.txt

14.Delete a stack

You can delete stacks using the name, so for the above example.

cfnassist -env Dev -build 1223 -rm templateFile

Note that the name of stack in cloudformation will include the Project, Environment and (optionally) the build number.

You can also delete a stack created with cfnassit using the following command:

cfnassist -env Dev -build 1223 -delete ./templateFile.json

This will delete the stack that was created from the templateFile.json file with the build number 1223.

15.Using VPC Tags

cfnassist will automatically populate a Tag on the VPC based on a simple convention for the Output section of a cloudformation script. For example having the following in your output section will cause a new tag called SUBNET to be created on the correct VPC for the current project/env combination. In this case the tag will contian the ID of a created subnet.

"Outputs" : { "SUBNET" : { "Value" : { "Ref":"testSubnet" }, "Description":"::CFN_TAG" }

You can also use a VPC Tag value as in input parameter, just use the same convention for the input parameter as above.

"testVPCTAG":{ "Type":"String", "Description":"::CFN_TAG" }

This example will try and find a TAG called testVPCTAG on the current VPC and inject it's value into the template.

16.Using Environemental Variables

You can pick up a input parameter value from an environmental variable using the following convention in the description.

"Parameters" : {
"nameOfEnvVar":{ "Type":"String", "Description":"::ENV" } }

This example will try and find a environmental variable called 'nameOfEnvVar' and inject it's value into the template using a parameter of the same name i.e. 'nameOfEnvVar'

17.Tidy up old stacks

USE WITH CARE - This deletes instances

You can automatically delete stacks created from the same template (i.e. created with different build numbers) if those stacks are no longer associated with an ELB.

cfnassist -env Dev -tidyOldStacks ./templateFile.json typeTag

Ihis will locate the ELB for the project/env using the tag CFN_ASSIST_TYPE to choose one if multiple are present, in this case the tage would need to be set to typeTag. Next all stacks created from the template templateFile.json are located and their instances scanned. If the stack has no instances associated with the ELB then it will be deleted.

18.Generate VPC diagrams

This will attempt to generate diagrams for your vpc, they are in the GraphViz format. Two diagrams will be generated for each VPC, one for the network configuration and one for the security.

Work in progess - please give feedback via github issues

cfnassist -diagrams targetFolder



19.Manage ELB Security Group access

This is helpful if you need to lock down access to a web site during development & testing while still allowing your current location to access it.

cfnassist -env Dev -allowCurrentIP web 80

This will update the Security Group for the Dev environment's ELB to allow access to port 80 from your current public IP. To revoke the access use this command (from the same location/public IP!)

cfnassist -env Dev -blockCurrentIP web 80

If need be you can use the aws console or cli tool to upadte the ELB secuity group, for example if you forget to revoke access before leaving a location.

If more than one ELB is found then cfnassist will check if the tag CFN_ASSIST_TYPE is present and matches the type tag you give above, if it is the tool will use that ELB, otherwise an error will be thrown.

cfnassist -env Dev -allowhost web hostname 80

This will update the Security Group for the Dev environment's ELB to allow access to port 80 from any of the hosts IPs. To revoke the access use this command

cfnassist -env Dev -blockhost web hostname 80

20.Stack Notifications

This can be very useful for notifying people or other software of updates to cloud formation.

Cfnassist with detect if there is a SNS topic called 'CFN_ASSIST_NOTIFICATIONS' available and accessible for the user. If so notifications are sent containing the stackname, status, user id and user name. Make sure the user has permissions to do the 'getuser' call on the AWS api. You can wire up SNS to email etc via AWS.

21.Auto populate availability zones

This allows auto population of the correct AZ names for the current region.

"Parameters" : { "zoneA":{ "Type":"String", "Description":"::CFN_ZONE_A" }, "zoneB":{ "Type":"String", "Description":"::CFN_ZONE_B" } }

This means you can more easily create portable templates that will work in different regions without change. In the above example zoneA and zoneB will be populated with the correct zone names for the current region.

22.Create a key pair

cfnassist -env Dev -keypair <filename>

This will create a key pair named after the current project and environment. A tag will be created on the VPC for the project/env that contains the keyname, the TAG is called 'keypairname'.

NOTE NEVER save a private key in a place where it could get checked into your source control,

The key will be named '__keypair'. If you provide a filename the private key will be saved in this file. If you don't give a filename the key will be saved in $HOME/.ssh/<projectName>_<env name>.pem

NOTE ALWAYS Keep your private keys safe

23.Manage cloudwatch logs

cfnassist -env Dev -logs 6

Down and save in files (named after cloudwatch log groups) the log events form the last N hours. The log groups need to be tagged with the appropriate CFN_ASSIST_ENV and CNF_ASSIST_PROJECT tags, see below.

cfnassist -env Dev -removeLogs 1

Delete cloudwatch log events/streams older than N Days.

NOTE Use with care, this is permanently delete the events

cfnassist -env UAT -tagLog logGroupName

Tags the given log group with CFN_ASSIST_ENV and CNF_ASSIST_PROJECT using the given values.