Boot Actions

Boot actions can be more accurately described as post-deployment file placement. This file placement can be leveraged to install actions for servers to take after the permanent OS is installed and the server is rebooted. Including custom or vendor scripts and a SystemD service to run the scripts on first boot or on all boots allows almost any action to be configured.

Boot Action Schema

Boot actions are configured via YAML documents included in the site topology definition. The schema for these YAML documents is described below.

  signaling: true
    - path: /save/file/here
      type: unit|file|pkg_list
      data: |
        inline data here
        - template
        - base64_decode
        - template
        - base64_encode
      permissions: 555

signaling is a boolean noting whether Drydock should expect a signal at the completion of this boot action. If set to true for a boot action that does not send a signal, it will elongate the deployment step and consider the boot action failed.

assets is a list of data assets. More details below on how each data asset is rendered.

node_filter is an optional filter for selecting to which nodes this boot action will apply. If no node filter is included, all nodes will receive the boot action. Otherwise it will be only the nodes that match the logic of the filter set. See Tasks for a definition of the node filter.

Rendering Data Assets

The boot action framework supports assets of several types. type can be unit or file or pkg_list.

  • unit is a SystemD unit, such as a service, that will be saved to path and enabled via systemctl enable [filename].
  • file is simply saved to the filesystem at path and set with permissions.
  • pkg_list is a list of packages

Data assets of type unit or file will be rendered and saved as files on disk and assigned the permissions as specified. The rendering process can follow a few different paths.

Referenced vs Inline Data

The asset contents can be sourced from either the in-document data field of the asset mapping or dynamically generated by requesting them from a URL provided in location. Currently Drydock supports the schemes of http, deckhand+http and promenade+http for referenced data.

Package List

For the pkg_list type, the data section is expected to be a YAML mapping with key: value pairs of package_name: version where package_name is a Debian package available in one of the configured repositories and version is a valid apt version specifier or a empty/null value. Null indicates no version requirement.

If using a referenced data source for the package list, Drydock expects a YAML or JSON document returned in the above format.


The boot action framework supports pipelines to allow for some dynamic rendering. There are separate pipelines for the location field to build the URL that referenced assets should be sourced from and the data field (or the data sourced from resolving the location field).

The location string will be passed through the location_pipeline before it is queried. This response or the data field will then be passed through the data_pipeline. The data entity will start the pipeline as a bytestring meaning if it is defined in the data field, it will first be encoded into a bytestring. Below are pipeline segments available for use.

Decode the data element from base64
Encode the data element in base64
Decode the data element from bytes to UTF-8 string
Encode the data element from a UTF-8 string to bytes

Treat the data element as a Jinja2 template and apply a node context to it. The defined context available to the template is below.

  •[network_name].ip - IP address of this node on network [network_name]
  •[network_name].cidr - CIDR of [network_name]
  •[network_name].dns_suffix - DNS suffix of [network_name]
  • node.hostname - Hostname of the node
  • node.domain - DNS Domain of the primary network on the node
  • node.tags - Sequence of tags assigned to this node
  • node.labels - Key, value pairs of both explicit and dynamic labels for this node
  • action.action_id - A ULID that uniquely identifies this boot action on this node. Can be used for signaling boot action result.
  • action.action_key - A random key in hex that authenticates API calls for signaling boot action result.
  • action.report_url - The URL that can be POSTed to for reporting boot action result.
  • action.design_ref - The design reference for the deployment that initiated the bootaction

Also available in the Jinja2 template is the urlencode filter to encode a string for inclusion in a URL.

Reporting Results

The assets put in place on a server can report the results of applying the boot action using the Drydock bootaction API. The report API URL and boot action key are both available via the template pipeline segment context. It is up to the boot action assets to implement the call back to the API for reporting whatever data the boot action desires.