feat(linstorvolumemanager): cache controller uri in a file

[Millefeuille42]

No description provided.

[Wescoeur]

I'm not sure that's necessary here. We can instead do a refactoring of the codebase:

• We will assume that the cache is valid 99% of the time.
• We can directly attempt to create a LINSTOR instance from the URI without checking anything using a plugin. This is the initial idea.
• I think we can implement a new static function on LinstorVolumeManager that is used to create an instance of the class using the cached value directly without any checks. If it fails, we rebuild the local cache and try again. This allows us to improve several smapi functions.
• There are a few edge cases left with this idea:
  • In some places we use the URI to create the journaler (linstor.KV) and to create a linstor object. We could try to use the cached URI without checks again and add a try/catch directly on these specific cases. In case of connection failure, we explicitly request the cache update.
  • I see one last edge case concerning the creation of a linstor instance using get_ips_from_xha_config_file, we could directly use the function to get the cached URI. In the worst can we can again fallback on the xha config file.

[Millefeuille42]

Edge cases are almost done. I pushed modification of the added functions 042014f and created the static method you suggested 0364eed. Could you please take a look at the current state of those functions to validate them before I start the refactor ?

[Wescoeur]

Sounds good from my POV. Feel free to continue when you have time. :)

[Wescoeur]

Suggested change

	def get_cached_controller_uri(ctx=None):
	try:
	with ctx if ctx else shared_reader(CONTROLLER_CACHE_PATH) as f:
	return f.read().strip()
	except FileNotFoundError:
	pass
	except Exception as e:
	util.SMlog('Unable to read controller URI cache file at `{}` : {}'.format(CONTROLLER_CACHE_PATH,e))
	def _read_controller_uri_from_file(f):
	try:
	return f.read().strip()
	except Exception as e:
	util.SMlog('Unable to read controller URI cache file at `{}`: {}'.format(CONTROLLER_CACHE_PATH, e))
	def read_controller_uri_cache():
	try:
	with shared_reader(CONTROLLER_CACHE_PATH) as f:
	return _read_controller_uri_from_file(f)
	except FileNotFoundError:
	pass
	except Exception as e:
	util.SMlog('Unable to read controller URI cache file at `{}`: {}'.format(CONTROLLER_CACHE_PATH, e))

[Millefeuille42]

done in 4f84f23

[Wescoeur]

Suggested change

	def delete_controller_uri_cache(ctx=None):
	try:
	with ctx if ctx else excl_writer(CONTROLLER_CACHE_PATH) as f:
	f.seek(0)
	f.truncate()
	except FileNotFoundError:
	pass
	except Exception as e:
	util.SMlog('Unable to delete uri cache file at `{}` : {}'.format(CONTROLLER_CACHE_PATH, e))
	def delete_controller_uri_cache():
	try:
	with excl_writer(CONTROLLER_CACHE_PATH) as f:
	f.seek(0)
	f.truncate()
	except FileNotFoundError:
	pass
	except Exception as e:
	util.SMlog('Unable to delete URI cache file at `{}`: {}'.format(CONTROLLER_CACHE_PATH, e))

[Millefeuille42]

done in 4f84f23

[Wescoeur]

Cannot add suggestion due to github limitation but:

def build_controller_uri_cache():
    uri = ''
    try:
        with excl_writer(CONTROLLER_CACHE_PATH) as f:
            uri = _read_controller_uri_from_file(f)
            if uri:
                return uri
            uri = _get_controller_uri()
            if not uri:
                for retries in range(9):
                    time.sleep(1)
                    uri = _get_controller_uri()
                    if uri:
                        break
            if uri:
                f.seek(0)
                f.write(uri)
                f.truncate()
    except FileNotFoundError:
        if os.path.exists(CONTROLLER_CACHE_DIRECTORY):
            raise
        os.makedirs(CONTROLLER_CACHE_DIRECTORY)
        os.chmod(CONTROLLER_CACHE_DIRECTORY, 0o700)
        return build_controller_uri_cache()
    except Exception as e:
        util.SMlog('Unable to write URI cache file at `{}` : {}'.format(CONTROLLER_CACHE_PATH, e))

    return uri

[Millefeuille42]

done in 1f6ffbb

[Wescoeur]

Suggested change

	def get_controller_uri():
	uri = get_cached_controller_uri()
	if not uri:
	uri = build_controller_uri_cache()
	return uri
	def get_controller_uri():
	uri = read_controller_uri_cache()
	if not uri:
	uri = build_controller_uri_cache()
	return uri

[Millefeuille42]

done in 4f84f23

[Wescoeur]

Suggested change

	uri = get_cached_controller_uri()
	uri = read_controller_uri_cache()

[Millefeuille42]

done in 4f84f23

[Wescoeur]

Replaced by: #121 .