Add support for HAProxy L7 checks

This change add configuration options to enable HTTP checks
to the HAProxy configuration, instead of the default TCP connection
checks.

Added pip.sh to fix blessings dependency.

Closes-Bug: #1880610
Change-Id: Id42370fe07a2bcbcf28993d44f943d2b5c142107

config.yaml

@@ -95,6 +95,23 @@ options:
     description: |
        Connect timeout configuration in ms for haproxy, used in HA
        configurations. If not provided, default value of 9000ms is used.
+  haproxy-check-http:
+    type: boolean
+    default: False
+    description: |
+      If True uses HTTP (Layer 7) checks for backends in haproxy, used in
+      haproxy-check-http-config.
+  haproxy-check-http-config:
+    type: string
+    default: |
+      option httpchk GET /healthcheck\nhttp-check expect status 200
+    description: |
+      Enables HTTP protocol to check on the servers health and consider 200
+      as response status code. This config can be changed accordingly with
+      the charm need. There are specific checks for ldap, psql, mysql and etc
+      that can be customized in this field.
+      NOTE: This config is used when haproxy-check-http is enabled.
+      See https://www.haproxy.com/documentation/hapee/latest/onepage/ for more details
   dns-ha:
     type: boolean
     default: False

pip.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+#
+# This file is managed centrally by release-tools and should not be modified
+# within individual charm repos.  See the 'global' dir contents for available
+# choices of tox.ini for OpenStack Charms:
+#     https://github.com/openstack-charmers/release-tools
+#
+# setuptools 58.0 dropped the support for use_2to3=true which is needed to
+# install blessings (an indirect dependency of charm-tools).
+#
+# More details on the beahvior of tox and virtualenv creation can be found at
+# https://github.com/tox-dev/tox/issues/448
+#
+# This script is wrapper to force the use of the pinned versions early in the
+# process when the virtualenv was created and upgraded before installing the
+# depedencies declared in the target.
+pip install 'pip<20.3' 'setuptools<50.0.0'
+pip "$@"

tox.ini

@@ -14,7 +14,7 @@ setenv = VIRTUAL_ENV={envdir}
          JUJU_REPOSITORY={envdir}/tmp/build
 passenv = http_proxy https_proxy
 install_command =
-  pip install {opts} {packages}
+  {toxinidir}/pip.sh install {opts} {packages}
 deps =
   -r{toxinidir}/requirements.txt
 whitelist_externals = /bin/true /bin/echo /bin/mkdir /bin/ln