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Michael Fitz-Payne c4ea439cc3 DEV: refactor cache_critical_dns for SRV RR awareness
Modify the cache_critical_dns script for SRV RR awareness. The new
behaviour is only enabled when one or more of the following environment
variables are present (and only for a host where the `DISCOURSE_*_HOST_SRV`
variable is present):
- `DISCOURSE_DB_HOST_SRV`
- `DISCOURSE_DB_REPLICA_HOST_SRV`
- `DISCOURSE_REDIS_HOST_SRV`
- `DISCOURSE_REDIS_REPLICA_HOST_SRV`

Some minor changes in refactor to original script behaviour:
- add Name and SRVName classes for storing resolved addresses for a hostname
- pass DNS client into main run loop instead of creating inside the loop
- ensure all times are UTC
- add environment override for system hosts file path and time between DNS
  checks mainly for testing purposes

The environment variable for `BUNDLE_GEMFILE` is set to enables Ruby to
load gems that are installed and vendored via the project's Gemfile.
This script is usually not run from the project directory as it is
configured as a system service (see
71ba9fb7b5/templates/cache-dns.template.yml (L19))
and therefore cannot load gems like `pg` or `redis` from the default
load paths. Setting this environment variable configures bundler to look
in the correct project directory during it's setup phase.

When a `DISCOURSE_*_HOST_SRV` environment variable is present, the
decision for which target to cache is as follows:
- resolve the SRV targets for the provided hostname
- lookup the addresses for all of the resolved SRV targets via the
  A and AAAA RRs for the target's hostname
- perform a protocol-aware healthcheck (PostgreSQL or Redis pings)
- pick the newest target that passes the healthcheck

From there, the resolved address for the SRV target is cached against
the hostname as specified by the original form of the environment
variable.

For example: The hostname specified by the `DISCOURSE_DB_HOST` record
is `database.example.com`, and the `DISCOURSE_DB_HOST_SRV` record is
`database._postgresql._tcp.sd.example.com`. An SRV RR lookup will return
zero or more targets. Each of the targets will be queried for A and AAAA
RRs. For each of the addresses returned, the newest address that passes
a protocol-aware healthcheck will be cached. This address is cached so
that if any newer address for the SRV target appears we can perform a
health check and prefer the newer address if the check passes.

All resolved SRV targets are cached for a minimum of 30 minutes in memory
so that we can prefer newer hosts over older hosts when more than one target
is returned. Any host in the cache that hasn't been seen for more than 30
minutes is purged.

See /t/61485.
2022-04-27 10:14:33 +10:00
.devcontainer FEATURE: Support for GitHub Codespaces development (#11440) 2020-12-08 21:35:15 -03:00
.github DEV: Add CI job that audits dependency licenses (#16568) 2022-04-26 14:09:42 -04:00
.vscode-sample DEV: Move vscode config files to .vscode-sample directory (#11943) 2021-02-03 14:14:39 +00:00
app FEATURE: Add in:messages search modifier (#16567) 2022-04-26 16:47:01 -04:00
bin DEV: Avoid $ globals (#15453) 2022-01-08 23:39:46 +01:00
config FEATURE: Scope search to PMs when in that context (#16528) 2022-04-26 14:43:09 -04:00
db FIX: Check if bookmarkable column exists before adding (#16497) 2022-04-19 12:01:18 +10:00
docs DEV: Add registerCustomLastUnreadUrlCallbackto plugin API (#16222) 2022-03-23 13:34:17 -04:00
images Replace README logo with PNG (#14044) 2021-08-13 14:23:49 -04:00
lib FEATURE: Add in:messages search modifier (#16567) 2022-04-26 16:47:01 -04:00
log
plugins DEV: use the only source for time shortcut options on all date pickers (#16366) 2022-04-21 15:49:11 +04:00
public FIX: Email styles for Gmail app dark mode (#16482) 2022-04-14 15:03:06 -04:00
script DEV: refactor cache_critical_dns for SRV RR awareness 2022-04-27 10:14:33 +10:00
spec FEATURE: Add in:messages search modifier (#16567) 2022-04-26 16:47:01 -04:00
test DEV: Minor linting fixes (#16359) 2022-04-02 21:15:38 +02:00
vendor DEV: Update Moment to 2.29.2 (#16423) 2022-04-11 13:27:24 -04:00
.editorconfig
.eslintignore DEV: Minor linting fixes (#16359) 2022-04-02 21:15:38 +02:00
.eslintrc DEV: Disallow Ember global usage (#16147) 2022-03-09 17:54:07 +01:00
.git-blame-ignore-revs DEV: the referenced commit bc97… was rebased into 445d… (#11626) 2021-01-07 08:14:54 +11:00
.gitattributes
.gitignore DEV: Add CI job that audits dependency licenses (#16568) 2022-04-26 14:09:42 -04:00
.licensed.yml DEV: Add CI job that audits dependency licenses (#16568) 2022-04-26 14:09:42 -04:00
.licensee.json DEV: Add CI job that audits dependency licenses (#16568) 2022-04-26 14:09:42 -04:00
.npmrc DEV: Prevent npm usage (#13945) 2021-08-04 22:04:58 +02:00
.prettierignore DEV: Ignore plugin YAML files. 2022-01-14 09:58:46 +08:00
.prettierrc DEV: upgrades dev config (#10588) 2020-09-04 13:33:03 +02:00
.rspec DEV: Automatically require 'rails_helper' in all specs (#16077) 2022-03-01 17:50:50 +00:00
.rspec_parallel
.rubocop.yml Revert "Bump rubocop-discourse to 2.3.0." 2020-07-24 13:18:49 +08:00
.ruby-gemset.sample
.ruby-version.sample Update .ruby-version.sample 2021-07-30 14:42:14 -04:00
.template-lintrc.js enable eol-last for eslint and ember-template-lint (#12678) 2021-04-12 17:22:00 -07:00
adminjs
Brewfile
config.ru
CONTRIBUTING.md
COPYRIGHT.md DEV: Absorb onebox gem into core (#12979) 2021-05-26 15:11:35 +05:30
d
discourse.sublime-project
Gemfile Revert "DEV: Update to Sprockets 4.0 (#16467)" (#16524) 2022-04-20 22:17:29 +01:00
Gemfile.lock Build(deps): Bump rubocop from 1.27.0 to 1.28.2 (#16549) 2022-04-25 11:47:12 +02:00
jsapp
lefthook.yml DEV: Lint SCSS with prettier in pre-commit (#15033) 2021-11-22 11:30:12 +10:00
LICENSE.txt DEV: Absorb onebox gem into core (#12979) 2021-05-26 15:11:35 +05:30
package.json DEV: Update Moment to 2.29.2 (#16423) 2022-04-11 13:27:24 -04:00
Rakefile FIX: Do not dump schema during production database migrations (#12785) 2021-04-21 16:26:20 +01:00
README.md DEV: Update browser policy to include iOS 12 (#16503) 2022-04-19 14:58:57 +01:00
translator.yml DEV: Add styleguide locale files to Crowdin (#10876) 2020-10-09 13:23:32 +11:00
yarn.lock DEV: Update Moment to 2.29.2 (#16423) 2022-04-11 13:27:24 -04:00

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