Alerts

Alerts are the types of conditions that will trigger Monika to send notifications. It is an array defined in the config file monika.yml like so.

1 probes:
2   - id: '1'
3     name: Name of the probe
4     requests:
5       - method: GET
6         url: https://github.com
7         alerts:
8           - assertion: response.size >= 10000
9             message: Response size is {{ response.size }}, expecting less than 10000

You can define two types of alerts: request alerts and probe alerts

Request Alerts

Request alerts are alerts configurations that are scoped under the requests key. Alerts defined under a specific request will run for that specific request only. Take a look at the example below:

1 probes:
2   - id: '1'
3     name: Name of the probe
4     requests:
5       - method: GET
6         url: https://github.com
7         alerts:
8           - assertion: response.status != 200
9             message: Status not 2xx # (This alert is only triggered for the github.com request)
10       - method: GET
11         url: https://gitlab.com
12         alerts:
13           - assertion: response.status != 200
14             message: Status not 2xx # (This alert is only triggered for the gitlab.com request)

Probe Alerts

Probe alerts are alerts configurations that are defined under the probe key. Alerts scoped under the probe key will run for all requests for that probe. Take a look at the example below:

1 probes:
2   - id: '1'
3     name: Name of the probe
4     requests:
5       - method: GET
6         url: https://github.com
7         alerts:
8           - assertion: response.status != 200
9             message: Status not 2xx # (This alert is only triggered for the github.com request)
10       - method: GET
11         url: https://gitlab.com
12         alerts:
13           - assertion: response.status != 200
14             message: Status not 2xx # (This alert is only triggered for the gitlab.com request)
15     alerts:
16       - assertion: response.time > 10000 # in milliseconds
17         message: Response time is longer than 10 seconds # (This alert is triggered for all request)

Alert Timing

Probes are performed after every interval, and alerts are generated after a specified threshold. Monika can perform probes once a second, therefore a theoretical maximum rate of one alert a second. Please keep in mind that there may be some delays to your network, notification channels (slack, email, etc), so your result will vary.

In general it will be something like:

 Alert resolution = interval period (s) x threshold + network_and_channel_latencies

From above, the theoretical maximum resolution is one second.

Alert Assertion

Assertion contains any arbitrary expression that will trigger alert when it returns a truthy value

1 alerts:
2   - assertion: response.status == 500

Inside the assertion expression you can get the response object.

These are values that are available:

• response.status: HTTP status code of the response
• response.time: the time it takes to perform a HTTP request
• response.size: size of the response in bytes
• response.headers: HTTP response headers
• response.body: HTTP response body (if content-type is JSON, it will be parsed automatically)

The response.headers and response.body can be queried further with object access syntax.

For example, to trigger alert when content-type is not json you may use

1 alerts:
2   - assertion: response.headers['content-type'] != "application/json"

Or to assertion value inside the body

1 alerts:
2   - assertion: response.body.data.todos[0].title != "Drink water"

Additionally you can have processing done in your queries. For instance, to ensure case insensitivity, you might want to convert to lowercase. It might look something like this:

1 alerts:
2   - assertion: has(lowerCase(response.body.status), "success")

These operators are available:

There are also several helper functions available:

• has(object, property): Checks whether an object has searched property.

  example: has(response.body, "data") checks if there is "data" property inside response.body

• lowerCase(string): Converts string to lowercase

  example: lowerCase(response.body.message) converts message string value to lowercase

• upperCase(string): Converts string to uppercase

  example: upperCase(response.body.message) converts message string value to uppercase

• startsWith(string, target): Checks if string starts with the given target string

  example: startsWith(response.body.message, "Hello") checks if message string value starts with "Hello"

• endsWith(string, target): Checks if string ends with the given target string

  example: startsWith(response.body.message, "world!") checks if message string value ends with "world!"

• includes(collection, value): Checks if value is in collection. If collection is a string, it's checked for a substring of value

  example 1: includes(response.body.prizes, "gold") checks if "gold" exists in the prizes array.

  example 2: includes(response.body.message, "ello") checks if "ello" is a substring of the message string.

• size(collection): Gets length of array or string values.

  example: size(response.body.data.items) gets the count of items.

• isEmpty(value): Checks if value is an empty object, empty array, empty string, null, or undefined.

  example: isEmpty(response.body.data) checks whether the data property is empty or not

Alert Message

1 alerts:
2   - assertion: response.status != 200
3     message: HTTP Status code is different, expecting 200

This is the message that is used in the sent notification.

Inside the message string, you can also get the response object similar to assertion by surrounding the expression with double curly braces like the example above.

Built-in Alerts

Monika will automatically issue an alert when it detects a probe is inaccessible. An incident and recovery alert will be sent to all configured notification channels. Note that explicit connection assertion and customized message strings are not yet supported.

Further reading

1. Probes
2. Notifications