Azure Synthetic Monitoring

Azure function to monitor internal and external service status, reporting to Application Insight in the following formats:

• availability events, named <prefix>-<app_name>-<api_name> further distinguished by the type defined in the configuration used as "run location" for the test
• custom event, using the name <prefix>-<app_name>-<api_name>-<type>. these events are queryable ising log insight and can be visualized using Grafana

Configuration

This application relies on a configuration structure stored on the configured table storage structured as follows:

Column Name	description	required
PartitionKey	string. name of the app and api being monitored, expressed using the format <app_name>-<api_name>	yes
RowKey	string. type of the api being monitored. same as type	yes
url	string. url to be monitored	yes
method	string, upper case. method to be used when invoking url	yes
body	json stringifyied. body of the to be provided during the request. Allowed only when method is PATCH, POST, DELETE, PUT	no
expectedCodes	json stringifyied string. list of string and ranges (eg "200-220") of accepted http status (considered a success for the availability metric)	yes
type	string. identified of the api type being called. suggested types: private, public	yes
checkCertificate	boolean string. if true, also checks the server's certificate (expiration, version)	yes
durationLimit	number. threshold, in milliseconds, over which a response time will trigger a failed availability test. to not be confused with HTTP_CLIENT_TIMEOUT env variable	yes
tags	json stringifyied. dictionary of tags to be added to the tracked metrics	yes
headers	json stringifyied. dictionary of headers to be sent in the http request	no
bodyCompareStrategy	strategy to be used when compating received response body to expectedBoddy. Possible values: contains, containsKeys, listOfTypes, typeOf	no
expectedBody	json stringifyied. expected body type/content. used in conjunction with bodyCompareStrategy	no

Note on the type: any value is accepted, it will be traced in the application insight availability panel as "runLocation". suggested values are:

• private: means that the api being tested is reached through internal network (vnet)
• public: means that the api being tested is reached through internet

Detail on compareStrategy

Method	Functionality	Applied to
contains	checks if all the fields defined in the expected body are present in the actual body, and if their value are equal (recursively). On object arrays, checks if the received array has exactly the same element of the expected, using this contains on each element for comparison. On primitive arrays, checks if all the expected elements are included n the received, using Array.includes() for comparison	objects
containsKeys	checks if all the fields defined in the expected body are present in the actual body, and if their value are of the expected type (recursively). Values associable to object keys: bool string number array, object. You can also define the array content type, using ["number"]	objects
listOfTypes	checks if the response is a list containing the types defined in the body field. Uses the containsKeys logic to check each element of the list	array
typeOf	checks if the response type is as expected. supports all types returned by javascript typeof	any

here's an example in json format to better understand the content

{
  "apiName": "post",
  "appName": "httpbin",
  "url": "https://httpbin.org/get",
  "type": "private",
  "method": "GET",
  "expectedCodes": [
    "200",
    "300-303"
  ],
  "headers": {
    "Content-Type": "application/json"
  },
  "body": {
    "name": "value"
  },
  "tags": {
    "description": "sample post request"
  }
}

Certificate check

When enabled, the application will check the certificate associated to the configured domain in addition to checking the configured api The certificate is expected to expire in 7 days or more for the metric to be considered "success". When checking the certificate, the suffix -cert will be appended to the "runLocation" field of the metric, and will be visualized in the Application Insight page alongside the other run locations configured (see type configuration field)

Env variables

name	description	required	default
APP_INSIGHT_CONNECTION_STRING	application insight connection string. where to publish availability metrics and custom events	yes	-
STORAGE_ACCOUNT_NAME	storage account name used to store the monitoring configuration	yes	-
STORAGE_ACCOUNT_KEY	storage account access key	yes	-
STORAGE_ACCOUNT_TABLE_NAME	table name used to store the monitoring configuration	yes	-
AVAILABILITY_PREFIX	prefix used in the custom metric and events names	no	synthetic
HTTP_CLIENT_TIMEOUT	response timeout used by the http client performing the availability requests	yes	-
HTTP_CONNECTION_TIMEOUT	connection timeout used by the http client performing the availability requests	yes	-
LOCATION	region name where this job is run	yes	-
CERT_VALIDITY_RANGE_DAYS	number of days before the expiration date of a certificate over which the check is considered success	yes	-

Deploy

To deploy this job you can use the module monitoring_function provided in terraform-azurerm-v3