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MODULES.md

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Module scructure

A module is a directory with files. Addon-operator searches for the modules directories in /modules or in the path specified by $MODULES_DIR variable. The module has the same name as the corresponding directory excluding the numeric prefix.

The file structure of the module’s directory:

/modules/001-simple-module
├── .helmignore
├── Chart.yaml
├── enabled
├── hooks
│   └── module-hooks.sh
├── README.md
├── templates
│   └── daemon-set.yaml
└── values.yaml
  • hooks — directory with hooks;
  • enabled — script that gets the status of module (is it enabled or not). See the modules discovery process;
  • Chart.yaml, .helmignore, templates — files for the Helm chart;
  • README.md — module description;
  • values.yaml – default values for chart in a special format.

Module name in this case is simple-module.

Notes on how Helm is used

values.yaml

Addon-operator does not use values.yaml as the only source of values for the chart. It generates a new file with a merged set of values (also mixing values from this file (see VALUES).

Chart.yaml

We recommend to define the version field in your Chart.yaml as "0.0.1" and use VCS to control versions. We also recommend to explicitly specify the name field even despite it is ignored: Addon-operator passes the module name to the Helm as a release name.

Releases deduplication

A module’s execution might be triggered by an event that does not change the parameters of the module (see modules discovery). Re-running Helm will lead to an "empty" release. To avoid this, Addon-operator compares values’ checksums and starts the installation of a Helm chart only if there are some changes.

Workarounds for Helm issues

Helm badly handles failed chart installations (PR#4871). A workaround has been added to Addon-operator to reduce the number of manual interventions in such situations: automatic deletion of the single failed release. In the future, in addition to this mechanism, we plan to add a few improvements to the interaction with Helm. In particular, we plan to port related algorithms (how the interaction with Helm is done) from werf — ROADMAP.

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