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dns-cache

dns-cache is a Python client side DNS caching framework utilising dnspython v1.15+ for DNS and supports various local key stores, and provides caching of lookup failures, and configurable expiration of cached responses.

Some reasons to use a client side cache include:

  • processing data containing many repeated invalid domains,
  • running a local DNS caching service is not practical or appropriate,
  • adding reporting of DNS activity performed within a job.

Installation

The recommended way to install dns-cache is by using pip as follows:

pip install dns-cache

Getting started

To quickly benefit from client side dns-caching in your existing application, install the system resolver.

import dns_cache
import requests

dns_cache.override_system_resolver()

for i in range(10):
     requests.get('http://www.coala.io/')

If you have a fast dns proxy, 10 requests will possibly show no performance improvement. Even 100 may not perform better in this contrived example.

However when many parts of a system are performing lookups on the same DNS records, or where sessions are being closed and new ones created and need to access the same DNS records, the difference becomes more noticable, especially in jobs which takes hours to run.

For long running jobs, use the min_ttl argument to increase the default if 5 minutes isnt sufficient. It can be set to dns_cache.NO_EXPIRY for a ttl of one week, which is not recommended except when accompanied with custom cache expiration logic.

Key stores

Multiple key stores are supported, and their dependencies need to added separately as required.

  1. pickle and pickle4 backport: dns_cache.pickle.PickableCache
  2. diskcache: dns_cache.diskcache.DiskCache
  3. stash.py: dns_cache.stash.StashCache
  4. sqlitedict: dns_cache.sqlitedict.SqliteDictCache
  5. disk_dict: dns_cache.disk_dict.DiskDictCache (Python 2.7 only)

stash.py support uses pickle or jsonpickle on Python 3, however only jsonpickle works on Python 2.7.

Caching additions

The following classes can be used separately or together.

  1. dns_cache.resolver.AggressiveCachingResolver: indexes all qnames in the response, increasing the number of keys, but reducing the number of requests and cached responses when several related records are requested, such as a HTTP redirect from www.foo.com to foo.com (or vis versa) where one is a CNAME point to the other.
  2. dns_cache.resolver.ExceptionCachingResolver: caches lookup failures.
  3. dns_cache.hosts.HostsCache: preloads hosts (e.g. /etc/hosts) into a cache

Note: dns_cache.override_system_resolver() can be used to install a custom resolver or cache, which may be derived from the above classes or your own implementation from scratch. It preloads /etc/hosts.

Similar projects

Python:

  1. velocity is a lighter weight approach, with a serious bug
  2. dnsplug, unfortunately not available on PyPI.

Other:

  1. dnscache (Go)
  2. native-dns-cache (Node)