Triggers

Triggers are responsible for performing actions when a new container version is found.

Triggers are enabled using environment variables.

DD_ACTION_{{ trigger_type }}_{{ trigger_name }}_{{ trigger_configuration_item }}=XXX
DD_NOTIFICATION_{{ trigger_type }}_{{ trigger_name }}_{{ trigger_configuration_item }}=XXX

Environment variable prefixes

Three prefixes are supported for trigger configuration:

All three prefixes are interchangeable -- they configure the same triggers. Use whichever reads best for your use case: DD_ACTION_* for update-action triggers (Docker, Docker Compose) and DD_NOTIFICATION_* for messaging triggers (Slack, SMTP, Discord, etc.), or use either for any trigger type.

When the same trigger property is set under multiple prefixes, the merge priority is DD_NOTIFICATION_* > DD_ACTION_* > DD_TRIGGER_* (highest wins).

Available triggers

Update actions:

• Docker -- Update containers via the Docker Engine API
• Docker Compose -- Update containers managed by Docker Compose

Messaging & notifications:

• Apprise -- Multi-provider notification relay
• Command -- Execute a shell command
• Discord -- Discord webhook
• Google Chat -- Google Chat webhook
• Gotify -- Gotify push notification
• HTTP -- Generic HTTP request
• IFTTT -- IFTTT webhook
• Kafka -- Apache Kafka topic
• Matrix -- Matrix room message
• Mattermost -- Mattermost webhook
• MQTT -- MQTT topic
• ntfy -- ntfy push notification
• Pushover -- Pushover notification
• Rocket.Chat -- Rocket.Chat webhook
• Slack -- Slack webhook
• SMTP -- Email notification
• Teams -- Microsoft Teams webhook
• Telegram -- Telegram bot message

Common trigger configuration

All implemented triggers, in addition to their specific configuration, also support the following common configuration variables. The table uses the DD_TRIGGER_* prefix for brevity, but DD_ACTION_* and DD_NOTIFICATION_* work identically (see Environment variable prefixes above).

Threshold reference

Any threshold can be suffixed with -no-digest to exclude digest-only updates (e.g. major-no-digest, minor-only-no-digest). Updates with an unknown update kind are always filtered out regardless of the threshold setting.

Notes

• RESOLVENOTIFICATIONS is currently implemented for Gotify (auto-deletes the notification message after a successful update). Other providers can be extended to support it.
• Some messaging triggers (Slack, Telegram, Teams, Matrix, Mattermost, Rocket.Chat, Google Chat) also support DISABLETITLE (default false) to send only the body without a title line.
• You can set DD_TRIGGER_{trigger_type}_THRESHOLD to define a default threshold for all triggers of the same type, e.g. DD_TRIGGER_NTFY_THRESHOLD=minor.
• Triggers are executed by ascending ORDER; when two triggers have the same ORDER, they are sorted by trigger id.
• Triggers sharing the same trigger name (e.g. docker.update and discord.update) can share THRESHOLD; if exactly one threshold value is defined among them, that value is used for the others unless they override it explicitly.
• Setting ONCE=false with MODE=batch gives a report with all pending updates on every run.
• MODE=digest accumulates update events in an in-memory buffer and flushes them as a single batch notification on the DIGESTCRON schedule. If the same container has multiple updates within the window, only the latest is included. Containers that are updated before the digest fires are automatically evicted from the buffer. Useful for daily email digests: DD_TRIGGER_SMTP_GMAIL_MODE=digest + DD_TRIGGER_SMTP_GMAIL_DIGESTCRON=0 8 * * *.

Notification Rules

Notification rules control which events fire which triggers. Each rule corresponds to an event type and has an enabled flag and an optional list of trigger IDs.

Dispatch behavior:

• update-available -- for backward compatibility, when its trigger list is empty all triggers fire (existing behavior is preserved). Once you assign specific triggers, only those fire.
• update-applied, update-failed, security-alert -- these require explicit trigger assignments. They are enabled by default but will not fire any trigger until you add trigger IDs to their rules.
• agent-disconnect -- disabled by default. Enable it and assign triggers to receive disconnect alerts. This event always fires regardless of the threshold setting.

Rules are managed via GET /api/v1/notifications and PATCH /api/v1/notifications/:id (update enabled and/or triggers fields), or through the Notifications view in the UI.

Event Types

Beyond the classic update-available event, triggers can fire on additional events:

• update-applied -- fires after a container is successfully updated by a Docker or Docker Compose trigger. Useful for audit or confirmation notifications.
• update-failed -- fires when an update fails or is rolled back. Carries the container name and error message.
• security-alert -- fires when the Update Bouncer detects critical or high vulnerabilities during a pre-update scan. Includes a vulnerability summary.
• agent-disconnect -- fires when a remote agent loses its connection. This event skips threshold checks (always fires).

Template Variable Reference

Template strings use ${expression} placeholders. Drydock provides two sets of variables depending on the trigger mode.

Simple mode variables

Legacy aliases (deprecated)

These aliases resolve to a single container property and will be removed in v1.6.0. Use the container.* equivalents instead.

Batch mode variables

Legacy alias (deprecated)

Expression syntax

Inside ${...} you can use:

• Property paths -- container.updateKind.kind
• Method calls -- local.substring(0, 15) (see allowed methods below)
• Ternary -- container.result.link ? container.result.link : "no link"
• Logical AND -- container.result && container.result.link
• String concatenation -- "Version: " + container.updateKind.remoteValue
• String and number literals -- "hello", 42

Allowed string methods: substring, slice, toLowerCase, toUpperCase, trim, trimStart, trimEnd, replace, split, indexOf, lastIndexOf, startsWith, endsWith, includes, charAt, padStart, padEnd, repeat, toString.

Examples

services:
  drydock:
    image: codeswhat/drydock
    ...
    environment:
      - DD_TRIGGER_SMTP_GMAIL_SIMPLETITLE=Container $${container.name} can be updated
      - DD_TRIGGER_SMTP_GMAIL_SIMPLEBODY=Container $${name} can be updated from $${local.substring(0, 15)} to $${remote.substring(0, 15)}

docker run \
  -e 'DD_TRIGGER_SMTP_GMAIL_SIMPLETITLE=Container ${container.name} can be updated' \
  -e 'DD_TRIGGER_SMTP_GMAIL_SIMPLEBODY=Container ${name} can be updated from ${local.substring(0, 15)} to ${remote.substring(0, 15)}'
  ...
  codeswhat/drydock