healthchecks/templates/docs/signalling_failures.md
2020-10-28 14:28:32 +02:00

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# Signalling failures
You can actively signal a failure to SITE_NAME by slightly changing the
ping URL: append either `/fail` or `/{exit-status}` to your normal ping URL.
The exit status should be a 0-255 integer. SITE_NAME will interpret
exit status 0 as success, and all non-zero values as failures.
Examples:
```bash
# Reports failure by appending the /fail suffix:
curl --retry 3 PING_URL/fail
# Reports failure by appending a non-zero exit status:
curl --retry 3 PING_URL/1
```
By actively signalling failures to SITE_NAME, you can minimize the delay from your
monitored service encountering a problem to you getting notified about it.
## Shell Scripts
The below shell script appends `$?` (a special variable which contains the
exit status of the last executed command) to the ping URL:
```bash
#!/bin/sh
/usr/bin/certbot renew
curl --retry 3 PING_URL/$?
```
## Python
Below is a skeleton code example in Python which signals a failure when the
work function returns an unexpected value or throws an exception:
```python
import requests
URL = "PING_URL"
def do_work():
# Do your number crunching, backup dumping, newsletter sending work here.
# Return a truthy value on success.
# Return a falsy value or throw an exception on failure.
return True
success = False
try:
success = do_work()
finally:
# On success, requests PING_URL
# On failure, requests PING_URL/fail
requests.get(URL if success else URL + "/fail")
```