Andrew Onischuk created AMBARI-3924:
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Summary: Resource management framework: resources should be
executed immediately
Key: AMBARI-3924
URL: https://issues.apache.org/jira/browse/AMBARI-3924
Project: Ambari
Issue Type: Bug
Reporter: Andrew Onischuk
Assignee: Andrew Onischuk
Fix For: 1.5.0
Attachments: AMBARI-3924.patch
Currently, RMF acts like puppet. All scripts are executed in 2 stages:
1) Interpretation: All variables, "if" and "switch" statements are resolved and
a list of resources is created
2) Execution: All resources are actually created/executed/modified in
asynchronous (puppet) or sequential (RMF) way
This approach is great because a system will be never left half-configured
because of undefined variable: interpretation step will fail, and execution
will not start.
Also, such approach is great for unit testing (we may check resource
definitions, staged for execution, without actually executing them)
But for our usage, such delayed execution produces few troubles:
- Due to delayed execution, we can not check results of command execution at
our python logic. For example, we can not check if a file contains some text
after we run Exec() statement. Of course, we may add yet another Exec()
statement with shell code, but it's a hack. Solution may look like adding a
callback function to Exec() resource syntax, but that affects simplicity and
usability.
- due to a previous reason, writing service status checks for services is hard.
Especially if "service <name> status" command does not return non zero exit
code when service is not running.
- Using debugger for python scripts is not trivial as we don't see results of
command execution immediately and have to dive into env.run() essentials.
h3. The proposal is:
- Resources should execute immediately after definition. Any issues like
undefined variables will be cached during development/QA testing and should not
appear at production clusters.
- env.run() call is not necessary now
- To preserve unit testing advantages, Environment constructor should accept
optional parameter "test_mode" (that defaults to false). If this parameter is
set to true, than resources are not executed, but are still added to internal
list inside Environment
- Other architecture details should remain as is (resources are defined and
executed within Environment context, list of defined resources is stored inside
Environment)
h3. Expected impact:
- Existing scripts for services probably will not require modifications (they
are ported from puppet that uses the same paradigm). In some cases, they may be
simplified.
- Custom command implementations and status check methods will be simpler
- RMF learning curve should become more flat
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