kryndex / lua-resty-dns-client

Lua DNS client, load balancer, and utility library

Overview

Lua library containing a dns client, several utilities, and a load-balancer.

The module is currently OpenResty only, and builds on top of the lua-resty-dns library

Features

• resolves A, AAAA, CNAME and SRV records, including port
• parses /etc/hosts
• parses /resolv.conf and applies LOCALDOMAIN and RES_OPTIONS variables
• caches dns query results in memory
• synchronizes requests (a single request for many requestors, eg. when cached ttl expires under heavy load)
• toip applies a local (weighted) round-robin scheme on the query results
• ring-balancer for round-robin and consistent-hashing approaches

Copyright and license

Copyright: (c) 2016-2017 Mashape, Inc.

Author: Thijs Schreijer

License: Apache 2.0

Testing

Tests are executed using busted, but because they run inside the resty cli tool, you must use the rbusted script.

History

0.6.2 (04-Sep-2017) Fixes and refactor

• Fix: balancer not returning hostname for named SRV entries. See issue #17
• Fix: fix an occasionally failing test
• Refactor: remove metadata from the records, instead store it in its own cache

0.6.1 (28-Jul-2017) Randomization adjusted

• Change: use a different randomizer for the ring-balancer to predictably recreate the balancer in the exact same state (adds the lrandom library as a new dependency)

0.6.0 (14-Jun-2017) Rewritten resolver core to resolve async

• Added: resolution will be done async whenever possible. For this to work a new setting has been introduced staleTtl which determines for how long stale records will returned while a query is in progress in the background.
• Change: BREAKING! several functions that previously returned and took a resolver object no longer do so.
• Fix: no longer lookup ip adresses as names if the query type is not A or AAAA
• Fix: normalize names to lowercase after query
• Fix: set last-success types for hosts-file entries and ip-addresses

0.5.0 (25-Apr-2017) implement SEARCH and NDOTS

• Removed: BREAKING! stdError function removed.
• Added: implemented the search and ndots options.
• Change: resolve no longer returns empty results or dns errors as a table but as lua errors (nil + error).
• Change: toip() and resolve() have an extra result; history. A table with the list of tried names/types/results.
• Fix: timeout and retrans options from resolv.conf were ignored by the client module.
• Fix: nameservers with an ipv6 address would not be used properly. Also added a flag enable_ipv6 (default == false) to enable the useage of ipv6 nameservers.

0.4.1 (21-Apr-2017) Bugfix

• Fix: cname record caching causing excessive dns queries, see Kong issue #2303.

0.4.0 (30-Mar-2017) Bugfixes

• Change: BREAKING! modified hash treatment, must now be an integer > 0
• Added: BREAKING! a retry counter to fall-through on hashed-retries (changes the getpeer signature)
• Fix: the MAXNS (3) was not honoured, so more than 3 nameservers would be parsed from the resolv.conf file. Fixes Kong issue #2290.
• Added: two convenience hash functions
• Performance: some improvements (pre-allocated tables for the slot lists)

0.3.2 (6-Mar-2017) Bugfixes

• Fix: Cleanup disabled addresses but did not delete them, causing errors when they were repeatedly added/removed
• Fix: potential racecondition when re-querying dns records
• Fix: potential memoryleak when a balancer object was released with a running timer

0.3.1 (22-Feb-2017) Bugfixes

• Kubernetes dns returns an SRV record for individual nodes, where the target is the same name again (hence causing a recursive loop). Now those entries will be removed, and if nothing is left, it will fail the SRV lookup, causing a fall-through to the next record type.
• Kubernetes tends to return a port of 0 if none is provided/set, hence the toip() function now ignores a port=0 and falls back on the port passed in.

0.3.0 (8-Nov-2016) Major breaking update

• breaking: renamed a lot of things; method names, module names, etc. pretty much breaks everything... also releasing under a new name
• feature: udp function setpeername added (client)
• fix: do not synchronize dns queries for ttl=0 requests (client)
• fix: full test coverage and accompanying fixes (ring-balancer)
• feature: auto-retry for failed dns queries (ring-balancer)
• feature: updating weights is now supported without removing/re-adding (ring-balancer)
• change: auto-retry interval configurable for failed dns queries (ring-balancer)
• change: max life-time interval configurable for ttl=0 dns records (ring-balancer)

0.2.1 (24-Oct-2016) Bugfix

• fix: toip() failed on SRV records with only 1 entry

0.2 (18-Oct-2016) Added the balancer

• fix: was creating resolver objects even if serving from cache
• change: change resolver order (SRV is now first by default) for dns servers that create both SRV and A records for each entry
• feature: make resolver order configurable
• feature: ring-balancer (experimental, no full test coverage yet)
• other: more test coverage for the dns client

0.1 (09-Sep-2016) Initial released version