Attaching Logs

ztn.sh healthchecks ping endpoints accept HTTP HEAD, GET and POST request methods.

When using HTTP POST, you can include an arbitrary payload in the request body. ztn.sh healthchecks will log the first 10 kilobytes (10 000 bytes) of the request body, so that you can inspect it later.

Logging Command Output

In this example, we run certbot renew, capture its output (both the stdout and stderr streams), and submit the captured output to ztn.sh healthchecks:

#!/bin/sh

m=$(/usr/bin/certbot renew 2>&1)
curl -fsS -m 10 --retry 5 --data-raw "$m" https://ping.ztn.sh/your-uuid-here

In Combination with the /fail and /{exit-status} Endpoints

We can extend the previous example and signal either success or failure depending on the exit code:

#!/bin/sh

m=$(/usr/bin/certbot renew 2>&1)
curl -fsS -m 10 --retry 5 --data-raw "$m" https://ping.ztn.sh/your-uuid-here/$?

Using Runitor

Runitor is a third party utility that runs the supplied command, captures its output and reports to ztn.sh healthchecks. It also measures the execution time and retries HTTP requests on transient errors. Best of all, the syntax is simple and clean:

runitor -uuid your-uuid-here -- /usr/bin/certbot renew

Sending Logs Without Signalling Success or Failure

You may sometimes want to log diagnostic information without altering the check's current state. ztn.sh healthchecks provides the /log endpoint just for that. When you send an HTTP POST request to this endpoint, ztn.sh healthchecks will log the event and display it in check's "Events" section, but will keep the check's state unchanged.

Handling More Than 10KB of Logs

While ztn.sh healthchecks can store a small amount of logs in a pinch, it is not specifically designed for that. If you run into the issue of logs getting cut off, consider the following options:

  • See if the logs can be made less verbose. For example, if you have a batch job that outputs a line of text per item processed, perhaps it can output a summary with the totals instead.
  • If the important content is usually at the end, submit the last 10KB instead of the first. Here is an example that submits the last 10KB of dmesg output:
#!/bin/sh

m=$(dmesg | tail --bytes=10000)
curl -fsS -m 10 --retry 5 --data-raw "$m" https://ping.ztn.sh/your-uuid-here
  • Finally, if it is critical to capture the entire log output, consider using a dedicated log aggregation service for capturing the logs.

Where to See Captured Logs

In the check's details page, Events section, click on individual events to see full event details, including the captured log information.

The Events section

In the dialog that opens, use the "Download Original" link to download the request body data, exactly as it was submitted to ztn.sh healthchecks:

The Ping Details dialog