Examples

Note

Examples are shown in YAML format for simplicity and because this is the preferred format when using the slacker CLI.

Tip

See also Rule Library for some real-world reusable rules.

The simplest possible webhooks table item is like so:

account: '123456789012'
channel: channels-table-reference
sourceId: 'arn:aws:sns:us-east-1:123456789012:my-topic'

This will pass all incoming messages on the specified SNS topic to the specified Slack channel, unmodified.

Slacker gets more useful with the addition of message rules to filter or transform incoming messages. The following examples relate to the rules list attribute in webhooks table items.

Text Message Examples

Consider the following text message:

ERROR: The wheels have fallen off 3 little red wagons

The following rule set would force the message to be discarded (dropped):

account: ...
channel: ...
sourceId: ...
rules:
  - '#': Comment -- ignored
    match: '^ERROR:.*wagons$'
    action: drop

The following rule set would:

• Discard messages about a small number of wagons suffering wheels detaching.
• Add different colour bars for more severe wheel loss on red and blue wagons but send the message unmodified. Messages about blue wagons will be diverted to a different Slack channel.
• Send a custom message for severe wheel loss on other coloured wagons.

account: ...
channel: ...
sourceId: ...
rules:
  - match: '^ERROR:.* fallen off (?P<count>[0-9]+) little [a-z]+ wagons'
    if: '{{ data.count | int < 4 }}'
    action: drop
  - '#': This rule only reached for matching messages with wagon count >= 4
    match: '^ERROR:.* fallen off [0-9]+ little (?P<colour>[a-z]+) wagons'
    if: '{{ data.colour == "red" }}'
    colour: '#ff0000'
    action: send
  - '#': This rule for blue wagons has an implicit send action
    match: '^ERROR:.* fallen off [0-9]+ little (?P<colour>[a-z]+) wagons'
    if: '{{ data.colour == "blue" }}'
    colour: '#0000ff'
    channel: still-got-the-blues
  - '#': This rule produces a custom message for odd colour wagons
    match: '^ERROR:.* fallen off (?P<count>[0-9]+) little (?P<colour>[a-z]+) wagons'
    template: |
      WANTED: {{ data.count }} {{ data.colour }} wagons with wheels

Object Message Examples

Consider the following message indicating the number, and colour, of wagons for which a wheel has fallen off.

{ "event": "wheels off", "count": 3, "wagon_colour": "red" }

This will be received by slacker as a string but will will be JSON decoded to an object.

The following rule set would force the message above to be discarded:

account: ...
channel: ...
sourceId: ...
rules:
  - '#': Comment -- ignored
    if: '{{ event == "wheels off" and count | int < 4 }}'
    action: drop

The following rule set would:

• Discard messages about a small number of wagons suffering wheels detaching.
• Add different colour bars for more severe wheel loss on red and blue wagons but send the message unmodified. Messages about blue wagons will be diverted to a different Slack channel.
• Send a custom message for severe wheel loss on other coloured wagons.

account: ...
channel: ...
sourceId: ...
rules:
  - if: '{{ data.event == "wheels off" and data.count | int < 4 }}'
    action: drop
  - '#': This rule only reached for matching messages with wagon count >= 4
    if: '{{ data.event == "wheels off" and data.colour == "red" }}'
    colour: '#ff0000'
    action: send
  - '#': This rule for blue wagons has an implicit send action
    if: '{{ data.event == "wheels off" and data.colour == "blue" }}'
    colour: '#0000ff'
    channel: still-got-the-blues
  - '#': This rule produces a custom message for odd colour wagons
    if: '{{ data.event == "wheels off" }}'
    template: |
      WANTED: {{ data.count }} {{ data.colour }} wagons with wheels

The following rule set would format object messages nicely and pass other messages through unchanged.

account: ...
channel: ...
sourceId: ...
rules:
  - template: |
      ```
      {{ data | tojson(4) }}
      ```

The following rule set would discard messages sent between 5pm and 6pm Sydney time:

account: ...
channel: ...
sourceId: ...
rules:
  - if: '{{ "17:00:00" <= current_time("Australia/Sydney") <= "18:00:00" }}'
    action: drop