feat: Configurable poll rate for check-for-changes.sh (#4450)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
Co-authored-by: Casper <casperklein@users.noreply.github.com>

CHANGELOG.md

@@ -6,6 +6,11 @@ All notable changes to this project will be documented in this file. The format
 
 > **Note**: Changes and additions listed here are contained in the `:edge` image tag. These changes may not be as stable as released changes.
 
+### Added
+
+- **Internal:**
+  - [`DMS_CONFIG_POLL`](https://docker-mailserver.github.io/docker-mailserver/v15.0/config/environment/#dms_config_poll) supports adjusting the polling rate (seconds) for the change detection service `check-for-changes.sh` ([#4450](https://github.com/docker-mailserver/docker-mailserver/pull/4450))
+
 ### Updates
 
 - **Documentation:**

docs/content/config/environment.md

@@ -360,6 +360,23 @@ Default: empty (no prefix will be added to e-mails)
 
     Add trailing white-space by quote wrapping the value: `SPAM_SUBJECT='[SPAM] '`
 
+##### DMS_CONFIG_POLL
+
+Defines how often DMS polls [monitored config files][gh::monitored-configs] for changes in the DMS Config Volume. This also includes TLS certificates and is often relied on for applying changes managed via `setup` CLI commands.
+
+- **`2`** => How often (in seconds) [change detection][gh::check-for-changes] is performed.
+
+!!! note "Decreasing the frequency of polling for changes"
+
+    Raising the value will delay how soon a change is detected which may impact UX expectations for responsiveness, but reduces resource usage when changes are rare.
+
+!!! info
+
+    When using `ACCOUNT_PROVISIONER=LDAP`, the change detection feature is presently disabled.
+
+[gh::check-for-changes]: https://github.com/docker-mailserver/docker-mailserver/blob/v15.0.0/target/scripts/check-for-changes.sh#L37
+[gh::monitored-configs]: https://github.com/docker-mailserver/docker-mailserver/blob/v15.0.0/target/scripts/helpers/change-detection.sh#L30-L42
+
 #### Rspamd
 
 ##### ENABLE_RSPAMD

target/scripts/check-for-changes.sh

@@ -211,7 +211,7 @@ function _rspamd_changes() {
 
 while true; do
   _check_for_changes
-  sleep 2
+  sleep "${DMS_CONFIG_POLL:-2}"
 done
 
 exit 0

target/scripts/startup/variables-stack.sh

@@ -149,6 +149,7 @@ function __environment_variables_general_setup() {
   _log 'trace' 'Setting miscellaneous environment variables'
 
   VARS[ACCOUNT_PROVISIONER]="${ACCOUNT_PROVISIONER:=FILE}"
+  VARS[DMS_CONFIG_POLL]="${DMS_CONFIG_POLL:=2}"
   VARS[FETCHMAIL_PARALLEL]="${FETCHMAIL_PARALLEL:=0}"
   VARS[FETCHMAIL_POLL]="${FETCHMAIL_POLL:=300}"
   VARS[GETMAIL_POLL]="${GETMAIL_POLL:=5}"