71 lines
2.5 KiB
ReStructuredText
71 lines
2.5 KiB
ReStructuredText
Execution stages
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================
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Description
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-----------
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When cdist is started, it passes through different stages.
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Stage 1: target information retrieval
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-------------------------------------
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In this stage information is collected about the target host using so called
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explorers. Every existing explorer is run on the target and the output of all
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explorers are copied back into the local cache. The results can be used by
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manifests and types.
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Stage 2: run the initial manifest
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---------------------------------
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The initial manifest, which should be used for mappings of hosts to types,
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is executed. This stage creates objects in a cconfig database that contains
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the objects as defined in the manifest for the specific host. In this stage,
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no conflicts may occur, i.e. no object of the same type with the same id may
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be created, if it has different parameters.
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Stage 3: object information retrieval
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-------------------------------------
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Every object is checked whether its type has explorers and if so, these are
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executed on the target host. The results are transferred back
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and can be used in the following stages to decide what changes need to be made
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on the target to implement the desired state.
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Stage 4: run the object manifest
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--------------------------------
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Every object is checked whether its type has a executable manifest. The
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manifest script may generate and change the created objects. In other words,
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one type can reuse other types.
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For instance the object __apache/www.example.org is of type __apache, which may
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contain a manifest script, which creates new objects of type __file.
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The newly created objects are merged back into the existing tree. No conflicts
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may occur during the merge. A conflict would mean that two different objects
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try to create the same object, which indicates a broken configuration.
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Stage 5: code generation
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------------------------
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In this stage for every created object its type is checked for executable
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gencode scripts. The gencode scripts generate the code to be executed on the
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target on stdout. If the gencode executables fail, they must print diagnostic
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messages on stderr and exit non-zero.
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Stage 6: code execution
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-----------------------
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For every object the resulting code from the previous stage is transferred to
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the target host and executed there to apply the configuration changes.
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Stage 7: cache
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--------------
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The cache stores the information from the current run for later use.
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Summary
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-------
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If, and only if, all the stages complete without errors, the configuration
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will be applied to the target.
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