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
• (weighted) round-robin balancer
• consistent-hashing balancer
• least-connections balancer

Copyright and license

Copyright: (c) 2016-2021 Kong, 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.

For troubleshooting purposes: see the /extra folder for how to parse logs

History

Versioning is strictly based on Semantic Versioning

Release process:

1. update the changelog below
2. update the rockspec file
3. generate the docs using ldoc .
4. commit and tag the release
5. upload rock to LuaRocks

6.0.2 (05-Jul-2021)

• Fix: validTtl should not be used for host-file entries. PR 134

6.0.1 (22-Jun-2021)

• Performance: reduce amount of timers on init_worker. PR 130

6.0.0 (05-Apr-2021)

• BREAKING: the round-robin balancing algorithm is now implemented in resty.dns.round_robin and has no consistent-hashing algorithm features, which are now all restricted to resty.dns.consistent_hashing. PR 123
• Added: option to enable or disable nameservers randomization. Note: this feature depends on the to-be-released feature in lua-resty-dns. PR 119

5.2.3 (19-Mar-2021)

• Fix: potential synchronisation issue in the least-connections balancer. PR 126

5.2.2 (11-Mar-2021)

• Fix: do not iterate over all the search domains when resolving an unambiguous fully-qualified domain name (FQDN), i.e. ended in a dot. PR 122

5.2.1 (21-Jan-2021)

• Fix: balancer DNS updates could go into a busy loop upon renewal. Reported as Kong issue #6739, fixed with PR 116.

5.2.0 (7-Jan-2021)

• Fix: now a single timer is used to check for expired records instead of one per host, significantly reducing the number of resources required for DNS resolution. PR 112

5.1.1 (7-Oct-2020)

• Dependency: Bump lua-resty-timer to 1.0

5.1.0 (28-Sep-2020)

• Fix: workaround for LuaJIT/ARM bug, see Issue 93.
• Fix: table reduction was calculated wrong. Not a "functional" bug, just causing slightly less agressive memory releasing.
• Added: alternative implementation of the consistent-hashing balancing algorithm, which does not rely on the addresses addition and removal order to build the same request distribution among different instances. See PR 97.

5.0.0 (14-May-2020)

• BREAKING: getPeer now returns the host-header value instead of the hostname that was used to add the address. This is only breaking if a host was added through addHost with an ip-address. In that case getPeer will no longer return the ip-address as the hostname, but will now return nil. See PR 89.
• Added: option useSRVname, if truthy then getPeer will return the name as found in the SRV record, instead of the hostname as added to the balancer. See PR 89.
• Added: callback return an extra parameter; the host-header for the address added/removed.
• Fix: using the module instance instead of the passed one for dns resolution in the balancer (only affected testing). See PR 88.

4.2.0 (23-Mar-2020)

• Change: export DNS source type on status report. See PR 86.

4.1.3 (24-Jan-2020)

• Fix: fix ttl-0 records issues with the balancer, see Kong issue Kong/kong#5477
  • the previous record was not properly detected as a ttl=0 record by checking on the __ttl0flag we now do
  • since the "fake" SRV record wasn't updated with a new expiry time the expiry-check-timer would keep updating that record every second

4.1.2 (10-Dec-2019)

• Fix: handle cases when lastQuery is nil, see PR 81 and PR 82.

4.1.1 (14-Nov-2019)

• Fix: added logging of try-list to the TCP/UDP wrappers, see PR 75.
• Fix: reduce logging noise of the requery timer

4.1.0 (7-Aug-2019)

• Fix: unhealthy balancers would not recover because they would not refresh the DNS records used. See PR 73.
• Added: automatic background resolving of hostnames, expiry will be checked every second, and if needed DNS (and balancer) will be updated. See PR 73.

4.0.0 (26-Jun-2019)

• BREAKING: the balancer callback is called with a new event; "health" whenever the health status of the balancer changes.
• BREAKING: renamed setPeerStatus to setAddressStatus to be in line with the new setHostStatus, and prevent confusion.
• Added: keep track of unavailable weight. Added the getStatus method to return health, of the entire balancer structure. Health itself is determined based on the new property healthThreshold.
• Added: prevention of cascading failures when balancer is unhealthy. Use the healthThreshold value to set when the balancer is considered unhealthy.
• Added: method setHostStatus, to set the availability/health state of all addresses belonging to a host at once.
• Fix: when an asyncquery failed to create the timer, it would silently ignore the error. Error is now being logged.

3.0.2 (8-Mar-2019) Bugfix

• Fix: callback for adding an address did not pass the address object, but instead passed the balancer object twice.

3.0.1 (5-Mar-2019) Bugfix

• Fix: "balancer is nil" error, see issue #49.

3.0.0 (7-Nov-2018) Refactor & least-connections balancer

• Refactor: split the balancer in a base class (handling DNS resolution) and the ring-balancer, implementing the algorithm.
• Added: new least-connections balancer
• Fix: since addresses could occasionally hold names instead of IP addresses, it could happen that a call to setPeerStatus was unsuccessful, because the IP address would not match the name in the address object. Now a handle is returned by getPeer.
• BREAKING: getPeer signature (and return values) changed, making this a breaking change.

2.2.0 (28-Aug-2018) Fixes and a new option

• Added: a new option validTtl that, if set, will forcefully override the ttl value of any valid answer received. Issue 48.
• Fix: remove multiline log entries, now encoded as single-line json. Issue 52.
• Fix: always inject a localhost value, even if not in /etc/hosts. Issue 54.
• Fix: added a workaround for Amazon Route 53 nameservers replying with a ttl=0 whilst the record has a non-0 ttl. Issue 56.

2.1.0 (21-May-2018) Fixes

• Fix: the round-robin scheme for the balancer starts at a randomized position to prevent all workers from starting with the same peer.
• Fix: the balancer no longer returns port = 0 for SRV records without a port, the default port is now returned.
• Fix: ipv6 nameservers with a scope in their address are not supported. This fix will simply skip them instead of throwing errors upon resolving. Fixes issue 43.
• Minor: improved logging in the balancer
• Minor: relax requery default interval for failed dns queries from 1 to 30 seconds.

2.0.0 (22-Feb-2018) Major performance improvement (balancer) and bugfixes

• BREAKING: improved performance and memory footprint for large balancers. 80-85% less memory will be used, while creation time dropped by 85-90%. Since the host:getPeer() function signature changed, this is a breaking change.
• Change: BREAKING the errors for cache-only lookup failures and empty records have been changed.
• Fix: do not fail initialization without nameservers.
• Fix: properly recognize IPv6 in square brackets from the /etc/hosts file.
• Fix: do not set success-type to types we're not looking for. Fixes Kong issue #3210.
• Fix: store records from the additional section in cache
• Fix: do not overwrite stale data in the client cache with empty records

1.0.0 (14-Dec-2017) Fixes and IPv6

• Change: BREAKING all IPv6 addresses are now returned with square brackets
• Fix: properly recognize IPv6 addresses in square brackets

0.6.3 (27-Nov-2017) Fixes and flagging unhealthy peers

• Added: flag to mark an address as failed/unhealthy, see setPeerStatus
• Added: callback to receive balancer updates; addresses added-to/removed-from the balancer (after DNS updates for example).
• fix: SRV record entries with a weight 0 are now supported
• fix: failure of the last hostname to resolve (balancer)

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 usage 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