Lambda function to check http endpoint wrapped in serverless project
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README.md

Lambda http check

Lambda function to check specific http endpoint, and report on it's availability.

Optionally, it can record metrics to CloudWatch.

Inputs

All inputs are either defined as environment variables or as part of event data. Event data will take priority over environment variables

ENDPOINT - url to be checked

METHOD - http method to use, defaults to GET

PAYLOAD - http payload, if POST or PUT used as method

TIMEOUT - timeout to use for http requests, defaults to 120s

HEADERS - list of headers to send to target server, defaults to empty list. Headers should be specified in

REPORT_RESPONSE_BODY - set to 1 if you wish to report on response body, 0 otherwise, 0 otherwise, defaults to 0

REPORT_AS_CW_METRICS - set to 1 if you wish to store reported data as CW custom metrics, 0 otherwise, defaults to 1

CW_METRICS_NAMESPACE - if CW custom metrics are being reported, this will determine their namespace, defaults to 'HttpCheck'

BODY_REGEX_MATCH - if CW custom metrics are being reported, this will enable ResponseBodyRegexMatch metric to be published as well, with value determined by success of matching response body against regular expression contained within this option

STATUS_CODE_MATCH - report whether http status code is equal to given status code or not. If this option is not present, it won't be reported upon. Defaults to empty

FAIL_ON_STATUS_CODE_MISMATCH - if checking for status code match treat mismatch as failure, ie report Available: 0

Outputs

By default, following properties will be rendered in output Json

Reason - Reason

Available - 0 or 1

TimeTaken - Time in ms it took to get response from remote server. Default timeout is 2 minutes for http requests.

StatusCode - Http Status Code

ResponseBody - Optional, by default this won't be reported

ResponseBodyRegexMatch - Optional, if BODY_REGEX_MATCH option is provided

StatusCodeMatch - Optional, if STATUS_CODE_MATCH options is provided

Dependencies

Lambda function is having no external dependencies by design, so no additional packaging steps are required for deploying it, such as doing pip install [libname]

CloudWatch Metrics

In order to get some metrics which you can alert on, REPORT_AS_CW_METRICS and CW_METRICS_NAMESPACE environment variables are used. Following metrics will be reported

  • Available - 0 or 1, whether response was received in timely manner, indicating problems with network, DNS lookup or server timeout

  • TimeTaken - Time taken to fetch response, reported in milliseconds

  • StatusCode - HTTP Status code received from server

  • ResponseBodyRegexMatch - optional this will report 1 or 0 if BODY_REGEX_MATCH option is specified. 1 is reported if response body matches regex provided, or 0 otherwise.

  • StatusCodeMatch - *optional& this will report 1 or 0 if STATUS_CODE_MATCH options is specified. 1 is reported if response status code matches code provided, or 0 otherwise

Deployment

You can either deploy Lambda manually, or through serverless project. If serverless is being chosen as method of deployments use command below, while making sure that you have setup proper access keys. For more information read here

Serverless framework version used during development is 1.23.0, but it is very likely that later versions will function as well

sls deploy

If you are setting up your Lambda function by hand, make sure it has proper IAM permissions to push Cloud Watch metrics data, and to write to CloudWatch logs

Testing

To test function locally with simple Google url (default), run following

sls invoke local  -f httpcheck

Optionally, for complicated example take a look at test/ipify.json file

$ sls invoke local  -f httpcheck -p test/ipify.json 
Failed to connect to https://api.ipify.org?format=json
<urlopen error _ssl.c:732: The handshake operation timed out>
Failed to publish metrics to CloudWatch:'TimeTaken'
Result of checking https://api.ipify.org?format=json
{
 "Available": 0,
 "Reason": "<urlopen error _ssl.c:732: The handshake operation timed out>"
}
{
    "Available": 0,
    "Reason": "<urlopen error _ssl.c:732: The handshake operation timed out>"
}

Debugging

If you wish to see debug output for http request, set HTTP_DEBUG environment variable to '1'. This can't be controlled through event payload.

Schedule execution

Pull requests are welcome to serverless project to deploy CloudWatch rules in order to schedule execution of Http Checking Lambda function.