Github user cestella commented on a diff in the pull request:
https://github.com/apache/metron/pull/673#discussion_r129865653
--- Diff: metron-deployment/packaging/ambari/README.md ---
@@ -0,0 +1,86 @@
+# Ambari Management Pack Development
+Typically, Ambari Management Pack development will be done in the Vagrant
environments. These instructions are specific to Vagrant, but can be adapted
for other environemnts (e.g. make sure to be on the correct nodes for server vs
agent files)
+
+
+# Adding a new property
+1. Add the property to the appropriate `*-env.xml` file found in
`METRON.CURRENT/configuration`.
+ ```
+ <property>
+ <name>new_property</name>
+ <description>New Property description</description>
+ <value>Default Value</value>
+ <display-name>New Property Pretty Name</display-name>
+ </property>
+ ```
+
+2. Reference the property in
`METRON.CURRENT/package/scriptes/params/params_linux.py`, unless it will be
used in Ambari's status command. It will be stored in a variable. The name
doesn't have to match, but it's preferred that it does.
+Make sure to use replace `metron-env` the correct `*-env` file, as noted
above.
+ ```
+ new_property = config['configurations']['metron-env']['new_property']
+ ```
+If this property will be used in the status command, instead make this
change in `METRON.CURRENT/package/scriptes/params/status_params.py`.
+Afterwards, in `params_linux.py`, reference the new property:
+ ```
+ new_property = status_params.new_property
+ ```
+This behavior is because Ambari doesn't send all parameters to the status,
so it needs to be explicitly provided.
+
+3. Ambari master services can then import the params as such
+
+ ```
+ from params import params
+ env.set_params(params)
+ ```
+
+4. The `*_commands.py` files receive the params as an input from the
master services. Once this is done, they can be accessed via the variable we
set above:
+ ```
+ self.__params.new_property
+ ```
+
+ Ambari also has a custom `format` function that can access properties
when producing strings as output:
+ ```
+ from resource_management.libraries.functions import format as
ambari_format
+ # ...
+ Foo(ambari_format("{new_property}-adjusted")),
+ ```
+
+## How to identify errors in MPack changes
+Typically, any errors are thrown at one of two times:
+
+1. Attempting to install Metron as a whole. These are typically service
level definition errors, not property errors. Logs will often be found in
`/var/log/ambari-server/ambari-server.log`. Often the log will indicate it was
unable to load a particular service or subservice with some more detail.
+2. Running the actual functionality. These typically tend to cause errors
in the UI at runtime. Logs are usually found in
`/var/log/ambari-agent/ambari-agent.log`.
+
+Unfortunately, because errors tend to occur at runtime, it's often
necessary to add things like logging statements, or even just throw errors to
print out in the Ambari UI.
+
+The primary solution to these is to look in the logs for exceptions, see
what's going wrong (Property doesn't exist? Malformed file couldn't be
loaded?), and adjust appropriately.
+
+## Testing changes without cycling Vagrant build
+To avoid spinning down and spinning back up Vagrant, we'll want to instead
modify the files Ambari uses directly.
+Ambari stores the Python files from the service in a couple places.
+
+Specifically, the server files live in
+```
+/var/lib/ambari-server/resources/mpacks/metron-ambari.mpack-0.4.0.0/common-services
+/var/lib/ambari-agent/cache/common-services
+```
+
+e.g. enrichment_commands.py can be found in:
+
+```
+/var/lib/ambari-server/resources/mpacks/metron-ambari.mpack-0.4.0.0/common-services/METRON/0.4.0/package/scripts/enrichment_commands.py
+/var/lib/ambari-agent/cache/common-services/METRON/0.4.0/package/scripts/enrichment_commands.py
+```
+
+A `find` command can also be useful in quickly locating the exact location
of a file, e.g.
+```
+[root@node1 ~]# find /var/lib/ -name enrichment_commands.py
+/var/lib/ambari-server/resources/mpacks/metron-ambari.mpack-0.4.0.0/common-services/METRON/0.4.0/package/scripts/enrichment_commands.py
+/var/lib/ambari-agent/cache/common-services/METRON/0.4.0/package/scripts/enrichment_commands.py
+```
+
+The steps to update are:
+
+1. Edit the file(s) with your changes. The ambari-agent file must be
edited, but generally better to update both for consistency.
--- End diff --
So, if the mpack fails to install due to my change and I make a
modification (potentially) correcting the error by modifying the python files
in `/var/lib` and restart the agent, that'll rerun the install?
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