Introduction to AIT Configuration

AIT uses a number of YAML (YAML Ain’t Markup Language) and JSON files for project configuration.

You must ensure that the AIT_CONFIG environment variable points to your config.yaml file in order for AIT to properly configure your project. Given the default AIT project structure you would have the following setup. This assumes you’ve set AIT_ROOT to the project’s root directory:

export AIT_CONFIG=$AIT_ROOT/config/config.yaml

What is YAML?

YAML is a data serialization language with a heavy focus on maintaining human-readability. The YAML Getting Started provides an overview of the structures supported.


AIT uses config.yaml to load configuration data for the command (cmddict), telemetry (tlmdict), Event Verification Record (evrdict), Binary Stream Capture (bsc), and Logging (logging) components.

  • cmddict - defines the location of the Command Dictionary YAML file
  • evrdict - defines the location of the Event Verification Record (EVR) Dictionary YAML file
  • tlmdict - defines the location of the Telemetry Dictionary YAML file
  • bsc - defines the location of the Binary Stream Capture (BSC) YAML configuration file.
  • logging - defines the name to be associated with the Logger component (defaults to ‘ait’) and the host to push the output syslog information (defaults to ‘localhost’)
  • data - specifies all of the data paths associated with the GDS that can further be referenced by AIT or mission-specific tools. The paths specified can use path variables to allow for value substitution based upon date, hostname, platform, or any other configurable variable. See the ait-create-dirs tool and Path Expansion and Variables section below for more details.

The filename paths should be considered relative to the location of config.yaml. If you have hostname specific configuration you can add another block of data. The default block is the fall back if a match cannot be found. Below is an example config.yaml file that defines the default configuration files for AIT.

AIT loads config.yaml on import. Here is an example config.yaml:

            filename: ../cmdhist.pcap
        directory: ../seq
        filename:  cmd.yaml

        filename:  evr.yaml

        filename:  tlm.yaml

        filename:  bsc.yaml

        name:      ait
        hostname:  yourCustomHostForLogging

    phase: 'dev'

            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/downlink/1553
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/downlink/bad
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/downlink/lehx
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/planning
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/sdos
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/uplink
            path: /gds/${phase}/data/${hostname}/%Y/%Y-%j/ats

If you want to look at the contents of config.yaml programmatically you can access it with:

>>> ait.config

You can read more about each component’s configuration and configuration-schema files in the component-specific pages.

Path Expansion and Variables

File and directory paths included in config.yaml can be specified with varying degrees of explicitness in order to allow for the most flexibility. Any file or directory path specified with a key of ‘directory’, ‘file’, ‘filename’, ‘path’, or ‘pathname’ will resolve according to the details below.

Absolute Path Expansion

In the case where an absolute path is not specified for a ‘file’, ‘filename’, ‘path’, or ‘pathname’, the following are handled:

  • path does not begin with ‘/’ (relative path) - the path or filename given is assumed from the AIT_CONFIG directory.
  • path begins with ‘~’ (User HOME directory) - the current user’s home directory is used

Variable Substitution

Variables can also be specified within the path in order to allow for more explicit configuration. The following rules apply:

  • Variables are extracted from the keys specified in the config.yaml.
  • Any variables you would like to access must be at the base-level of the default, host, or platform:
    phase:      'dev'
    mission:    'oco3'
    instrument: 'pma'
  • The variable values must be a string or list of strings:
    phase:      'dev'
    mission:    'oco3'
    instrument: ['pma', 'icc', 'ecc']
  • Variables can be specified in a path using the following syntax

# For example
path: /${phase}/${mission}/${instrument}
  • There are currently 2 default variables whose values are automatically generated, and they can be accessed without specifying them in config.yaml.
    • ${year} - current year
    • ${doy} - current day of year
    • ${hostname} - hostname of machine where AIT is running
    • ${platform} - platform of machine where AIT is running


If we have the following specified in config.yaml:

    phase:      'dev'
    mission:    'oco3'
            path: /${phase}/${hostname}/%Y-%j/data1
            path: /${phase}/${hostname}/%Y-%j/data2

If the machine hostname = ‘oco3-gds1’, and today is day 300 in 2016, we can programmatically access these paths:

>>> for k, v in ait.config._datapaths.items():
>>>     print "%s - %s" % (k ,v)
data1 - /dev/oco3-gds1/2016-300/data1
data2 - /dev/oco3-gds1/2016-300/data2

See ait-create-dir software for more details on path substitution and how it can be leveraged.

YAML Idiosyncrasies

While YAML is generally very user-friendly, every tool has its rough edges. The AIT team has done its best to help you avoid these where possible. However, it may still be worth investigating potential roadblocks as you use YAML more. There is an excellent resource that the developers at SaltStack have put together on YAML idosyncrasies that is worth reading. It should help you avoid any potential problems in your YAML configuration.