CFNgin Config File

CFNgin makes use of a YAML formatted config file to define the different CloudFormation stacks that make up a given environment.

The configuration file has a loose definition, with only a few top-level keywords. Other than those keywords, you can define your own top-level keys to make use of other YAML features like anchors & references to avoid duplicating config. (See YAML anchors & references for details)

Top Level Keywords


You can provide a namespace to create all stacks within. The namespace will be used as a prefix for the name of any stack that CFNgin creates.

In addition, this value will be used to create an S3 bucket that CFNgin will use to upload and store all CloudFormation templates.

In general, this is paired with the concept of Environments to create a namespace per environment.

namespace: ${namespace}

Namespace Delimiter

By default, CFNgin will use - as a delimiter between your namespace and the declared stack name to build the actual CloudFormation stack name that gets created. Since child resources of your stacks will, by default, use a portion of your stack name in the auto-generated resource names, the first characters of your fully-qualified stack name potentially convey valuable information to someone glancing at resource names. If you prefer to not use a delimiter, you can pass the namespace_delimiter top-level keyword in the config as an empty string.

See the CloudFormation API Reference for allowed stack name characters

S3 Bucket

CFNgin, by default, pushes your CloudFormation templates into an S3 bucket and points CloudFormation at the template in that bucket when launching or updating your stacks. By default it uses a bucket named stacker-${namespace}, where the namespace is the namespace provided the config.

If you want to change this, provide the cfngin_bucket top-level keyword in the config.

The bucket will be created in the same region that the stacks will be launched in. If you want to change this, or if you already have an existing bucket in a different region, you can set the cfngin_bucket_region to the region where you want to create the bucket.

If you want CFNgin to upload templates directly to CloudFormation, instead of first uploading to S3, you can set cfngin_bucket to an empty string. However, note that template size is greatly limited when uploading directly. See the CloudFormation Limits Reference.

Persistent Graph

Each time CFNgin is run, it creates a dependency graph of Stacks. This is used to determine the order in which to execute them. This graph can be persisted between runs to track the removal of Stacks the config file.

When a stack is present in the persistent graph but not in the graph constructed from the config file, CFNgin will delete the stack from CloudFormation. This takes effect during both build and destroy actions.

The persistent graph is also used with the graph command where it is merged with the graph constructed from the config file.

To enable persistent graph, set persistent_graph_key to a unique value that will be used to construct the path to the persistent graph object in S3. This object is stored in the CFNgin S3 Bucket which is also used for CloudFormation templates. The fully qualified path to the object will look like the below.



It is recommended to enable versioning on the CFNgin S3 Bucket when using persistent graph to have a backup version in the event something unintended happens. A warning will be logged if this is not enabled.

If CFNgin creates an S3 Bucket for you when persistent graph is enabled, it will be created with versioning enabled.


When choosing a value for persistent_graph_key, it is vital to ensure the value is unique for the namespace being used. If the key is a duplicate, stacks that are not intended to be destroyed will be destroyed.

When executing an action that will be modifying the persistent graph (build or destroy), the S3 object is “locked”. The lock is a tag applied to the object at the start of one of these actions. The tag-key is cfngin_lock_code and the tag-value is UUID generated each time a command is run. In order for CFNgin to lock a persistent graph object, the tag must not be present on the object. For CFNgin to act on the graph (modify or unlock) the value of the tag must match the UUID of the current CFNgin session. If the object is locked or the code does not match, an error will be raised and no action will be taken. This prevents two parties from acting on the same persistent graph object concurrently which would create a race condition.


A persistent graph object can be unlocked manually by removing the cfngin_lock_code tag from it. This should be done with caution as it will cause any active sessions to raise an error.

Persistent Graph Example


namespace: example
cfngin_bucket: cfngin-bucket
persistent_graph_key: my_graph  # .json - will be appended if not provided


  "first_stack": [],
  "removed_stack": [


Given the above config file and persistent graph, when running runway deploy, the following will occur.

  1. The {"Key": "cfngin_lock_code", "Value": "123456"} tag is applied to s3://cfngin-bucket/persistent_graphs/example/my_graph.json to lock it to the current session.

  2. removed_stack is deleted from CloudFormation and deleted from the persistent graph object in S3.

  3. first_stack is updated in CloudFormation and updated in the persistent graph object in S3 (incase dependencies change).

  4. new_stack is created in CloudFormation and added to the persistent graph object in S3.

  5. The {"Key": "cfngin_lock_code", "Value": "123456"} tag is removed from s3://cfngin-bucket/persistent_graphs/example/my_graph.json to unlock it for use in other sessions.

Module Paths

When setting the classpath for Blueprints/hooks, it is sometimes desirable to load modules from outside the default sys.path (e.g., to include modules inside the same repo as config files).

Adding a path (e.g. ./) to the sys_path top-level keyword will allow modules from that path location to be used.

Service Role

By default CFNgin doesn’t specify a service role when executing changes to CloudFormation stacks. If you would prefer that it do so, you can set service_role to be the ARN of the role that CFNgin should use when executing CloudFormation changes.

This is the equivalent of setting RoleARN on a call to the following CloudFormation api calls: CreateStack, UpdateStack, CreateChangeSet.

See the AWS documentation for AWS CloudFormation Service Roles.

Remote Packages

The package_sources top-level keyword can be used to define remote sources for Blueprints (e.g., retrieving src/runway/blueprints on github at tag v1.3.7).

The only required key for a git repository config is uri, but branch, tag, & commit can also be specified.

    - uri:
    - uri:
      tag: 1.0.0
        - src/runway/blueprints
    - uri:
      branch: staging
    - uri:
      commit: 12345678

If no specific commit or tag is specified for a repo, the remote repository will be checked for newer commits on every execution of CFNgin.

For .tar.gz & zip archives on s3, specify a bucket & key.

    - bucket: mycfngins3bucket
      key: archives/
        - blueprints
    - bucket: anothers3bucket
      key: public/public-blueprints-v2.tar.gz
      requester_pays: true
    - bucket: yetanothers3bucket
      key: sallys-blueprints-v1.tar.gz
      # use_latest defaults to true - will update local copy if the
      # last modified date on S3 changes
      use_latest: false

Local directories can also be specified.

    - source: ../vpc

Use the paths option when subdirectories of the repo/archive/directory should be added to CFNgins’s sys.path.

Cloned repos/archives will be cached between builds; the cache location defaults to ~/.runway_cache but can be manually specified via the cfngin_cache_dir top-level keyword.

Remote Configs

Configuration YAMLs from remote configs can also be used by specifying a list of configs in the repo to use.

    - uri:
        - vpc.yaml

In this example, the configuration in vpc.yaml will be merged into the running current configuration, with the current configuration’s values taking priority over the values in vpc.yaml.

Dictionary Stack Names & Hook Paths

To allow remote configs to be selectively overridden, stack names & hook paths are defined as dictionaries.

    path: runway.cfngin.hooks.route53.create_domain:
    required: true
    enabled: true
    class_path: cfngin_blueprints.vpc.VPC
    locked: false
    enabled: true
    class_path: cfngin_blueprints.bastion.Bastion
    locked: false
    enabled: true

Pre & Post Hooks

Many actions allow for pre & post hooks. These are python functions/methods that are executed before, and after the action is taken for the entire config. Hooks can be enabled or disabled, per hook. Only the following actions allow pre/post hooks:

  • build (keywords: pre_build, post_build)

  • destroy (keywords: pre_destroy, post_destroy)

There are a few reasons to use these, though the most common is if you want better control over the naming of a resource than what CloudFormation allows.

The keyword is a dictionary with the following keys:


the python import path to the hook.


If set, and the hook returns data (a dictionary), the results will be stored in the context.hook_data with the data_key as its key.


Whether to stop execution if the hook fails.


Whether to execute the hook every CFNgin run. Default: True. This is a bool that grants you the ability to execute a hook per environment when combined with a variable pulled from an environment file.


A dictionary of arguments to pass to the hook with support for lookups. Note that lookups that change the order of execution, like output, can only be used in a post hook but hooks like rxref are able to be used with either pre or post hooks.

An example using the create_domain hook for creating a route53 domain before the build action:

    path: runway.cfngin.hooks.route53.create_domain
    required: true
    enabled: true

An example of a hook using the create_domain_bool variable from the environment file to determine if the hook should run. Set create_domain_bool: true or create_domain_bool: false in the environment file to determine if the hook should run in the environment CFNgin is running against:

    path: runway.cfngin.hooks.route53.create_domain
    required: true
    enabled: ${create_domain_bool}

An example of a custom hooks using various lookups in it’s arguments:

      ami: ${ami [<region>@]owners:self,888888888888,amazon name_regex:server[0-9]+ architecture:i386}
      user_data: ${file parameterized-64:file://some/path}
      db_endpoint: ${rxref some-stack::Endpoint}
      subnet: ${xref some-stack::Subnet}
      db_creds: ${ssmstore us-east-1@MyDBUser}
      bucket: ${dynamodb us-east-1:TestTable@TestKey:TestVal.BucketName}
      bucket_region: ${envvar AWS_REGION}  # this variable is set by Runway
        - ${file plain:file://some/path}

      nlb: ${output nlb-stack::Nlb}  # output can only be used as a post hook


CloudFormation supports arbitrary key-value pair tags. All stack-level, including automatically created tags, are propagated to resources that AWS CloudFormation supports. See AWS CloudFormation Resource Tags Type for more details. If no tags are specified, the cfngin_namespace tag is applied to your stack with the value of namespace as the tag value.

If you prefer to apply a custom set of tags, specify the top-level keyword tags as a map.


  "hello": world
  "my_tag:with_colons_in_key": ${dynamic_tag_value_from_my_env}
  simple_tag: simple value

If you prefer to have no tags applied to your stacks (versus the default tags that CFNgin applies), specify an empty map for the top-level keyword.

tags: {}


Mappings are dictionaries that are provided as Mappings to each CloudFormation stack that CFNgin produces.

These can be useful for providing things like different AMIs for different instance types in different regions.

      NAT: ami-ad227cc4
      ubuntu1404: ami-74e27e1c
      bastion: ami-74e27e1c
      NAT: ami-290f4119
      ubuntu1404: ami-5189a661
      bastion: ami-5189a661

These can be used in each Blueprint/stack as usual.


Lookups allow you to create custom methods which take a value and are resolved at build time. The resolved values are passed to the Blueprint before it is rendered. For more information, see the Lookups documentation.

CFNgin provides some common lookups, but it is sometimes useful to have your own custom lookup that doesn’t get shipped with Runway. You can register your own lookups by defining a lookups key.


The key name for the lookup will be used as the type name when registering the lookup. The value should be the path to a valid lookup handler.

You can then use these within your config.

conf_value: ${custom some-input-here}


This is the core part of the config - this is where you define each of the stacks that will be deployed in the environment. The top-level keyword stacks is populated with a dictionary, each representing a single stack to be built.

They key used in the dictionary of stacks is used as the logical name of the stack. The value here must be unique within the config. If no stack_name is provided, the value here will be used for the name of the CloudFormation stack.

A stack has the following keys:


The python class path to the Blueprint to be used. Specify this or template_path for the stack.


Path to raw CloudFormation template (JSON or YAML). Specify this or class_path for the stack. Path can be specified relative to the current working directory (e.g. templates stored alongside the Config), or relative to a directory in the python sys.path (i.e. for loading templates retrieved via packages_sources).


A short description to apply to the stack. This overwrites any description provided in the Blueprint. See:


A dictionary of Variables to pass into the Blueprint when rendering the CloudFormation template. Variables can be any valid YAML data structure.


(optional) If set to true, the stack is locked and will not be updated unless the stack is passed to CFNgin via the --force flag. This is useful for risky stacks that you don’t want to take the risk of allowing CloudFormation to update, but still want to make sure get launched when the environment is first created. When locked, it’s not necessary to specify a class_path or template_path.


(optional) If set to false, the stack is disabled, and will not be built or updated. This can allow you to disable stacks in different environments.


(optional) When running an update in non-interactive mode, if a stack has protected set to true and would get changed, CFNgin will switch to interactive mode for that stack, allowing you to approve/skip the change.


(optional) a list of other stacks this stack requires. This is for explicit dependencies - you do not need to set this if you refer to another stack in a Parameter, so this is rarely necessary.


(optional) a list of other stacks or targets that require this stack. It’s an inverse to requires.


(optional) a dictionary of CloudFormation tags to apply to this stack. This will be combined with the global tags, but these tags will take precedence.


(optional) If provided, this will be used as the name of the CloudFormation stack. Unlike name, the value doesn’t need to be unique within the config, since you could have multiple stacks with the same name, but in different regions or accounts. (note: the namespace from the environment will be prepended to this)


(optional): If provided, specifies the path to a JSON formatted stack policy that will be applied when the CloudFormation stack is created and updated. You can use stack policies to prevent CloudFormation from making updates to protected resources (e.g. databases). See:


(optional): If provided, specifies the behavior for when a stack is in CREATE_IN_PROGRESS or UPDATE_IN_PROGRESS. By default, CFNgin will raise an exception if the stack is in an IN_PROGRESS state. You can set this option to wait and CFNgin will wait for the previous update to complete before attempting to update the stack.

Stacks Example

Here’s an example used to create a VPC:

  - name: vpc-example
    class_path: blueprints.vpc.VPC
    locked: false
    enabled: true
      InstanceType: t2.small
      SshKeyName: default
      ImageName: NAT
      AZCount: 2

Custom Log Formats

By default, CFNgin uses the following log_formats:

  info: "[%(asctime)s] %(message)s"
  color: "[%(asctime)s] \033[%(color)sm%(message)s\033[39m"
  debug: "[%(asctime)s] %(levelname)s %(threadName)s %(name)s:%(lineno)d(%(funcName)s): %(message)s"

You may optionally provide custom log_formats. In this example, we add the environment name to each log line.

  info: "[%(asctime)s] ${environment} %(message)s"
  color: "[%(asctime)s] ${environment} \033[%(color)sm%(message)s\033[39m"

You may use any of the standard Python logging module format attributes when building your log_formats.


Variables are values that will be passed into a Blueprint before it is rendered. Variables can be any valid YAML data structure and can leverage Lookups to expand values at build time.

The following concepts make working with variables within large templates easier:

YAML anchors & references

If you have a common set of variables that you need to pass around in many places, it can be annoying to have to copy and paste them in multiple places. Instead, using a feature of YAML known as anchors & references, you can define common values in a single place and then refer to them with a simple syntax.

For example, say you pass a common domain name to each of your stacks, each of them taking it as a Variable. Rather than having to enter the domain into each stack (and hopefully not typo’ing any of them) you could do the following:

domain_name: &domain

Now you have an anchor called domain that you can use in place of any value in the config to provide the value You use the anchor with a reference.

  - name: vpc
    class_path: blueprints.vpc.VPC
      DomainName: *domain

Even more powerful is the ability to anchor entire dictionaries, and then reference them in another dictionary, effectively providing it with default values.

common_variables: &common_variables
  InstanceType: m3.medium
  AMI: ami-12345abc

Now, rather than having to provide each of those variables to every stack that could use them, you can just do this instead.

  - name: vpc
    class_path: blueprints.vpc.VPC
      << : *common_variables
      InstanceType: c4.xlarge # override the InstanceType in this stack

Using Outputs as Variables

Since CFNgin encourages the breaking up of your CloudFormation stacks into entirely separate stacks, sometimes you’ll need to pass values from one stack to another. The way this is handled in CFNgin is by having one stack provide Outputs for all the values that another stack may need, and then using those as the inputs for another stack’s Variables. CFNgin makes this easier for you by providing a syntax for Variables that will cause CFNgin to automatically look up the values of Outputs from another stack in its config. To do so, use the following format for the Variable on the target stack.

MyParameter: ${output OtherStack::OutputName}

Since referencing Outputs from stacks is the most common use case, output is the default lookup type. For more information see Lookups.

In this example config - when building things inside a VPC, you will need to pass the VpcId of the VPC that you want the resources to be located in. If the vpc stack provides an Output called VpcId, you can reference it easily.

domain_name: my_domain &domain

  - name: vpc
    class_path: blueprints.vpc.VPC
      DomainName: *domain
  - name: webservers
    class_path: blueprints.asg.AutoscalingGroup
      DomainName: *domain
      VpcId: ${output vpc::VpcId} # gets the VpcId Output from the vpc stack

Note: Doing this creates an implicit dependency from the webservers stack to the vpc stack, which will cause CFNgin to submit the vpc stack, and then wait until it is complete until it submits the webservers stack.


A pretty common use case is to have separate environments that you want to look mostly the same, though with some slight modifications. For example, you might want a production and a staging environment. The production environment likely needs more instances, and often those instances will be of a larger instance type. Environments allow you to use your existing CFNgin config, but provide different values based on the environment file chosen on the command line. For more information, see the Environments documentation.