27. Execution stages

27.1. Description

When cdist is started, it passes through different stages.

27.2. Stage 1: target information retrieval

In this stage information is collected about the target host using so called explorers. Every existing explorer is run on the target and the output of all explorers are copied back into the local cache. The results can be used by manifests and types.

27.3. Stage 2: run the initial manifest

The initial manifest, which should be used for mappings of hosts to types, is executed. This stage creates objects in a cconfig database that contains the objects as defined in the manifest for the specific host. In this stage, no conflicts may occur, i.e. no object of the same type with the same id may be created, if it has different parameters.

27.4. Stage 3: object information retrieval

Every object is checked whether its type has explorers and if so, these are executed on the target host. The results are transferred back and can be used in the following stages to decide what changes need to be made on the target to implement the desired state.

27.5. Stage 4: run the object manifest

Every object is checked whether its type has a executable manifest. The manifest script may generate and change the created objects. In other words, one type can reuse other types.

For instance the object __apache/www.example.org is of type __apache, which may contain a manifest script, which creates new objects of type __file.

The newly created objects are merged back into the existing tree. No conflicts may occur during the merge. A conflict would mean that two different objects try to create the same object, which indicates a broken configuration.

27.6. Stage 5: code generation

In this stage for every created object its type is checked for executable gencode scripts. The gencode scripts generate the code to be executed on the target on stdout. If the gencode executables fail, they must print diagnostic messages on stderr and exit non-zero.

27.7. Stage 6: code execution

For every object the resulting code from the previous stage is transferred to the target host and executed there to apply the configuration changes.

27.8. Stage 7: cache

The cache stores the information from the current run for later use.

27.9. Summary

If, and only if, all the stages complete without errors, the configuration will be applied to the target.