healthchecks/templates/docs/bash.md

Shell Scripts

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

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

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

Here's what each curl parameter does:

-m <seconds>

Maximum time in seconds that you allow the whole operation to take.

--retry <num>

If a 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).

Signalling Failure from Shell Scripts

You can append /fail to any ping URL and use the resulting URL to actively signal a failure. The following example:

• runs /usr/bin/certbot renew
• if the certbot command is successful (exit code 0), sends HTTP GET to PING_URL
• otherwise, sends HTTP GET to PING_URL/fail

#!/bin/sh

# Payload here:
/usr/bin/certbot renew
# Ping SITE_NAME
curl -m 10 --retry 5 "PING_URL$([ $? -ne 0 ] && echo -n /fail)"

Logging Command Output

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

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

#!/bin/sh

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

Auto-provisioning New Checks

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

#!/bin/bash

API_KEY=your-api-key-here

# 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 SITE_ROOT/api/v1/checks/  -H "X-Api-Key: $API_KEY" -d "$PAYLOAD"  | jq -r .ping_url`

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