Merge ~jugmac00/launchpad:how-to-check-availability-of-launchpad-frontends into launchpad:master

[Jürgen Gmach]

Add "Checking availability of Launchpad frontends" how-to

[Colin Watson (cjwatson)]

review: Approve

diff --git a/doc/how-to/checking-availability-of-launchpad-frontends.rst b/doc/how-to/checking-availability-of-launchpad-frontends.rst
new file mode 100644
index 0000000..cca8034
--- /dev/null
+++ b/doc/how-to/checking-availability-of-launchpad-frontends.rst
@@ -0,0 +1,36 @@
+============================================
+Checking availability of Launchpad frontends
+============================================
+
+
+Launchpad is using round-robin DNS to load balance requests among the
+frontends.
+
+So in order to check the availability of the frontends,
+you need to get a list of all frontends and then check them individually.
+
+Get list of frontends
+=====================
+
+.. code-block:: shell-session
+
+    $ host launchpad.net
+
+    launchpad.net has address 185.125.189.223
+    launchpad.net has address 185.125.189.222
+    launchpad.net has IPv6 address 2620:2d:4000:1001::8003
+    launchpad.net has IPv6 address 2620:2d:4000:1001::8004
+    launchpad.net mail is handled by 10 mx.launchpad.net.
+
+Check individual frontend
+=========================
+
+.. code-block:: shell-session
+
+    $ curl --resolve launchpad.net:443:185.125.189.222 https://launchpad.net/ 
+
+
+Further information
+===================
+
+https://everything.curl.dev/usingcurl/connections/name#provide-a-custom-ip-address-for-a-name
diff --git a/doc/how-to/index.rst b/doc/how-to/index.rst
index 9bdff11..80a4c6d 100644
--- a/doc/how-to/index.rst
+++ b/doc/how-to/index.rst
@@ -46,3 +46,4 @@ Operating Canonical's instances
    resurrect-dogfood
    restarting-services-on-dogfood
    deploying-configuration-changes
+   checking-availability-of-launchpad-frontends