caching.md

ANTA is a streamlined Python framework designed for efficient interaction with network devices. This section outlines how ANTA incorporates caching mechanisms to collect command outputs from network devices.

Configuration

By default, ANTA utilizes aiocache's memory cache backend, also called SimpleMemoryCache. This library aims for simplicity and supports asynchronous operations to go along with Python asyncio used in ANTA.

The _init_cache() method of the AntaDevice abstract class initializes the cache. Child classes can override this method to tweak the cache configuration:

def _init_cache(self) -> None:
    """
    Initialize cache for the device, can be overridden by subclasses to manipulate how it works
    """
    self.cache = Cache(cache_class=Cache.MEMORY, ttl=60, namespace=self.name, plugins=[HitMissRatioPlugin()])
    self.cache_locks = defaultdict(asyncio.Lock)

The cache is also configured with aiocache's HitMissRatioPlugin plugin to calculate the ratio of hits the cache has and give useful statistics for logging purposes in ANTA.

Cache key design

The cache is initialized per AntaDevice and uses the following cache key design:

<device_name>:<uid>

The uid is an attribute of AntaCommand, which is a unique identifier generated from the command, version, revision and output format.

Each UID has its own asyncio lock. This design allows coroutines that need to access the cache for different UIDs to do so concurrently. The locks are managed by the self.cache_locks dictionary.

Mechanisms

By default, once the cache is initialized, it is used in the collect() method of AntaDevice. The collect() method prioritizes retrieving the output of the command from the cache. If the output is not in the cache, the private _collect() method will retrieve and then store it for future access.

How to disable caching

Caching is enabled by default in ANTA following the previous configuration and mechanisms.

There might be scenarios where caching is not wanted. You can disable caching in multiple ways in ANTA:

1. Caching can be disabled globally, for ALL commands on ALL devices, using the --disable-cache global flag when invoking anta at the CLI:

   anta --disable-cache --username arista --password arista nrfu table

2. Caching can be disabled per device, network or range by setting the disable_cache key to True when defining the ANTA Inventory file:

   anta_inventory:
     hosts:
     - host: 172.20.20.101
       name: DC1-SPINE1
       tags: ["SPINE", "DC1"]
       disable_cache: True  # Set this key to True
     - host: 172.20.20.102
       name: DC1-SPINE2
       tags: ["SPINE", "DC1"]
       disable_cache: False # Optional since it's the default
   
     networks:
     - network: "172.21.21.0/24"
       disable_cache: True
   
     ranges:
     - start: 172.22.22.10
       end: 172.22.22.19
       disable_cache: True

   This approach effectively disables caching for ALL commands sent to devices targeted by the disable_cache key.

3. For tests developers, caching can be disabled for a specific AntaCommand or AntaTemplate by setting the use_cache attribute to False. That means the command output will always be collected on the device and therefore, never use caching.

Disable caching in a child class of AntaDevice

Since caching is implemented at the AntaDevice abstract class level, all subclasses will inherit that default behavior. As a result, if you need to disable caching in any custom implementation of AntaDevice outside of the ANTA framework, you must initialize AntaDevice with disable_cache set to True:

class AnsibleEOSDevice(AntaDevice):
  """
  Implementation of an AntaDevice using Ansible HttpApi plugin for EOS.
  """
  def __init__(self, name: str, connection: ConnectionBase, tags: set = None) -> None:
      super().__init__(name, tags, disable_cache=True)