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:
A command hook that exposes the current stack's AWS credentials to the shell command:
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.
The same as above but using the hex encoding.
See also
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