Shell Scripts

You can easily add Aryas-HealthChecks monitoring to a shell script. All you have to do is make an HTTP request at an appropriate place in the script. curl and wget are two common command-line HTTP clients you can use.

# Sends an HTTP GET request with curl:
curl -m 10 --retry 5

# Silent version (no stdout/stderr output unless curl hits an error):
curl -fsS -m 10 --retry 5 -o /dev/null

Here's what each curl parameter does:

-m <seconds>
Maximum time in seconds that you allow the whole operation to take.
--retry <num>
If an HTTP request fails, retry up to this many times. By default, curl uses an increasing delay between each retry (1s, 2s, 4s, 8s, ...). See also --retry-delay.
-f, --fail
Makes curl treat non-200 responses as errors.
-s, --silent
Silent or quiet mode. Hides the progress meter, but also hides error messages.
-S, --show-error
Re-enables error messages when -s is used.
-o /dev/null
Redirect curl's stdout to /dev/null (error messages still go to stderr).

Signaling Failure from Shell Scripts

You can append /fail or /{exit-status} to any ping URL and use the resulting URL to actively signal a failure. The exit status should be a 0-255 integer. Aryas-HealthChecks will interpret exit status 0 as success and all non-zero values as failures.

The following example runs /usr/bin/certbot renew, and uses the $? variable to look up its exit status:


# Payload here:
/usr/bin/certbot renew
# Ping Aryas-HealthChecks
curl -m 10 --retry 5$?

Logging Command Output

When pinging with HTTP POST, you can put extra diagnostic information in the request body. If the request body looks like a valid UTF-8 string, Aryas-HealthChecks will accept and store the first 10KB of the request body.

In the below example, certbot's output is captured and submitted via HTTP POST:


m=$(/usr/bin/certbot renew 2>&1)
curl -fsS -m 10 --retry 5 --data-raw "$m"

Auto-provisioning New Checks

This example uses Aryas-HealthChecks Management API to create a check "on the fly" (if it does not already exist) and retrieve its ping URL. Using this technique, you can write services that automatically register with Aryas-HealthChecks the first time they run.



# Check's parameters. This example uses system's hostname for check's name.
PAYLOAD='{"name": "'`hostname`'", "timeout": 60, "grace": 60, "unique": ["name"]}'

# Create the check if it does not exist.
# Grab the ping_url from JSON response using the jq utility:
URL=`curl -s  -H "X-Api-Key: $API_KEY" -d "$PAYLOAD"  | jq -r .ping_url`

# Finally, send a ping:
curl -m 10 --retry 5 $URL