docs: Add doc on using tideways

Author: tdgroot

docs/best-practices/performance/using-tideways.md

@@ -0,0 +1,53 @@
+---
+title: Using Tideways
+---
+
+# Using Tideways
+
+[Tideways](https://www.tideways.com/) is a profiling tool .....
+
+## Enabling Tideways
+
+Enabling the Tideways integration is very easy, it's only a few steps.
+This can be done in the CLI (command-line interface) of your Hypernode or with the [Control Panel](https://my.hypernode.com/).
+
+### Using the CLI
+
+First you need to log in to your Hypernode with SSH.
+After logging in, run the following commands:
+
+```console
+app@abcdef-example-magweb-cmbl:~$ hypernode-systemctl settings tideways_api_key my-tideways-api-key
+Operation was successful and is being processed. Please allow a few minutes for the settings to be applied. Run 'livelog' to see the progress.
+app@abcdef-example-magweb-cmbl:~$ hypernode-systemctl settings tideways_enabled True
+Operation was successful and is being processed. Please allow a few minutes for the settings to be applied. Run 'livelog' to see the progress.
+```
+
+### Using the Control Panel
+
+## Tideways with Varnish
+
+If you are using Varnish in front of your application, you can use the
+`X-Tideways-Profiler` header to pass the profiling information to the backend
+application. This is useful if you want to profile a specific request, but
+don't want to enable profiling for all requests.
+
+To enable this feature, you need to add the following configuration to your
+Varnish configuration:
+
+```vcl
+if (req.esi_level > 0) {
+    # ESI request should not be included in the profile.
+    # Instead you should profile them separately, each one
+    # in their dedicated profile.
+    # Removing the Tideways header avoids to trigger the profiling.
+    # Not returning let it go trough your usual workflow as a regular
+    # ESI request without distinction.
+    unset req.http.X-Tideways-Profiler;
+}
+
+# bypass if tideways request
+if (req.http.X-Tideways-Profiler && client.ip ~ profile) {
+    return (pass);
+}
+```