Lab A.3: update_pool.py¶

Task 1 – Review update_pool.py¶

1. Open update_pool.py in Notepad++
2. We will review the code. For brevity we have removed lines that are common with previous examples:

pool = mgmt.tm.ltm.pools.pool.load(partition=args.partition, name=args.pool_name)

pp.pprint("Current: %s=%s" % (args.attribute, getattr(pool, args.attribute)))

These lines load the pool from the device and print the current value of the attribute specified on the the command line. The second line is a little bit tricky because the SDK dynamically populates the objects attributes based on the type of object (pool, virtual server, etc.). Normally we could just use something like ‘pool.loadBalancingMode’ to get the current lb-method for the pool, however, since this script implements a way to change ANY attribute in the object we have to dynamically substitute the attribute name at run-time. To do this we use the getattr() python built-in function to resolve the mapping at runtime and return the value of the attribute specified on the command line.

kwargs = {args.attribute: args.value}

This line creates a new python dictionary with one entry specifying a key-value pair using the command line arguments. For example if you were updated the loadBalancingMode attribute to ‘least-connections-member’ the dictionary would look like {“loadBalancingMode”:”least-connections-member”}

pool.update(**kwargs)

The first line updates the pool we loaded previously with the new value for the attribute. The **kwargs argument to the update() method triggers a special mechanism in python called ‘keyword unpacking’ which allows us to pass the attribute to be updated to the update() method.

pool.refresh()
pp.pprint("New: %s=%s" % (args.attribute, getattr(pool, args.attribute)))

The first line refreshes the data in the object from the BIG-IP device. The second line prints this refreshed information to the console so the user can verify the update completed successfully.

Task 2 – Run update_pool.py¶

1. In the command prompt type python update_pool.py 10.1.1.4 test_pool loadBalancingMode least-connections-member and examine the output:

   

2. You can manually verify the load balancing method was changed via TMUI or by re-running read_pool.py (it’s not required since the line that prints the new value forces a refresh() )

3. Experiment with changing other pool attributes