Built-in hooks

You can use hooks to execute actions at specific stages of stack deploy and undeploy operations. Takomo has two built-in hooks, and you can also implement your own.

In a stack configuration, you choose which type of hook to use by providing value to the type property. You also need to give a name for each hook. In addition to these two mandatory properties, each hook type may have its own set of additional properties.

Command hook

The command hook executes the specified shell command.

Properties

Here are the properties of the Command hook:

Key	Required	Type	Description
type	yes	string	Type of the hook, this must be cmd.
name	yes	string	Name of the hook.
command	yes	string	Shell command to execute.
cwd	no	string	Path to the working directory from where the shell command is executed. Relative to the current project directory.
exposeStackCredentials	no	boolean	Make the current stack's AWS credentials available for the shell command. Defaults to false.
exposeStackRegion	no	boolean	Make the current stack's region available for the shell command. Defaults to false.
capture	no	string	Controls how to capture the output of the executed shell command. By default, all output is captured. To capture only the last line, set this to last-line.

Environment variables available in the shell command

The following environment variables are available in the shell command:

Name	Description
TKM_COMMAND_STAGE	The current stack operation stage.
TKM_COMMAND_OPERATION	The current stack operation.
TKM_COMMAND_STATUS	The current stack operation status, not present in before stage
AWS_ACCESS_KEY_ID	If exposeStackCredentials is true, this will hold the access key id of credentials of the current stack.
AWS_SECRET_ACCESS_KEY	If exposeStackCredentials is true, this will hold the secret access key of credentials of the current stack.
AWS_SESSION_TOKEN	If exposeStackCredentials is true, this will hold the session token of credentials of the current stack.
AWS_SECURITY_TOKEN	If exposeStackCredentials is true, this will hold the session token of credentials of the current stack.
AWS_DEFAULT_REGION	If exposeStackRegion is true, this will hold the region of the current stack.
TKM_HOOK_{hook-name}	Values returned from previous hooks are exposed in environment variables where the {hook-name} placeholder is replaced with the hook's name. Hooks whose name has unsafe characters not compatible with a pattern /^[a-zA-Z_]+[a-zA-Z0-9_]*$/ are not exposed and a warning is logged instead.

Any output the hook prints to the stdout is captured and exposed to other hooks.

Examples

A command hook that runs a simple shell command:

- name: my-hook
  type: cmd
  command: echo 'hello world'

A command hook that exposes the current stack's AWS credentials to the shell command:

- name: my-another-hook
  type: cmd
  exposeStackCredentials: true
  command: aws sts get-caller-identity

Checksum hook

The checksum hook calculates a checksum from a specified directory. The checksum is calculated recursively, i.e. all files and directories under the specified directory are included in the checksum.

Properties

Here are the properties of the Checksum hook:

Key	Required	Type	Description
type	yes	string	Type of the hook, this must be checksum
name	yes	string	Name of the hook
dir	yes	string	Path to the directory from where the checksum should be calculated. The path can be absolute or relative to the project directory.
encoding	no	string	Encoding used to encode the calculated checksum. Supported values are base64 (default) and hex.

Examples

Calculate a checksum from a directory lambda/scripts located in the project directory.

- name: my-checksum
  type: checksum
  dir: lambda/scripts

The same as above but using the hex encoding.

- name: my-hex-checksum
  type: checksum
  dir: lambda/scripts
  encoding: hex

See also

• Configuring hooks in stack configuration