Merge ~hloeung/content-cache-charm:http2 into content-cache-charm:master

[Haw Loeung]

Set/lower tcp_notsent_lowat to optimise HTTP/2 prioritisation.

See https://blog.cloudflare.com/http-2-prioritization-with-nginx/

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Barry Price (barryprice)]

LGTM +1

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 84b08ef9ea4bdabc07f60277f8af65b3cefcde89

diff --git a/.gitignore b/.gitignore
index c740bf5..4ee9909 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,5 +8,6 @@
 __pycache__/
 builds/
 deps/
+htmlcov/
 repo-info
 revision
diff --git a/reactive/content_cache.py b/reactive/content_cache.py
index d396779..93c72ca 100644
--- a/reactive/content_cache.py
+++ b/reactive/content_cache.py
@@ -488,6 +488,10 @@ def configure_sysctl():
             congestion_control = 'bbr'
         context['net_ipv4_tcp_congestion_control'] = congestion_control
 
+    # Set or lower tcp_notsent_lowat to optimise HTTP/2 prioritisation.
+    # https://blog.cloudflare.com/http-2-prioritization-with-nginx/
+    context['net_ipv4_tcp_notsent_lowat'] = '16384'
+
     base = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
     env = jinja2.Environment(loader=jinja2.FileSystemLoader(base))
     template = env.get_template('templates/sysctl_conf.tmpl')
diff --git a/templates/sysctl_conf.tmpl b/templates/sysctl_conf.tmpl
index a9f65f8..8904c5a 100644
--- a/templates/sysctl_conf.tmpl
+++ b/templates/sysctl_conf.tmpl
@@ -2,6 +2,9 @@
 # Taken from main Ubuntu Archive servers. Mostly for dealing with LFP.
 net.ipv4.tcp_congestion_control={{ net_ipv4_tcp_congestion_control }}
 {% endif -%}
+{% if net_ipv4_tcp_notsent_lowat -%}
+net.ipv4.tcp_notsent_lowat = {{ net_ipv4_tcp_notsent_lowat }}
+{% endif -%}
 {% if net_core_default_qdisc -%}
 net.core.default_qdisc={{ net_core_default_qdisc }}
 {% endif %}
diff --git a/tests/unit/files/sysctl_core_default_qdisc.conf b/tests/unit/files/sysctl_core_default_qdisc.conf
index c043b68..4cf9e97 100644
--- a/tests/unit/files/sysctl_core_default_qdisc.conf
+++ b/tests/unit/files/sysctl_core_default_qdisc.conf
@@ -1,3 +1,4 @@
+net.ipv4.tcp_notsent_lowat = 16384
 net.core.default_qdisc=fq
 
 
diff --git a/tests/unit/files/sysctl_core_default_qdisc_none.conf b/tests/unit/files/sysctl_core_default_qdisc_none.conf
index 3712507..b324a4d 100644
--- a/tests/unit/files/sysctl_core_default_qdisc_none.conf
+++ b/tests/unit/files/sysctl_core_default_qdisc_none.conf
@@ -1,3 +1,4 @@
+net.ipv4.tcp_notsent_lowat = 16384
 
 
 # Tune the TCP stack for Fast Failure Detection
diff --git a/tests/unit/files/sysctl_net_tcp_congestion_control.conf b/tests/unit/files/sysctl_net_tcp_congestion_control.conf
index fc5e418..bfebc3a 100644
--- a/tests/unit/files/sysctl_net_tcp_congestion_control.conf
+++ b/tests/unit/files/sysctl_net_tcp_congestion_control.conf
@@ -1,5 +1,6 @@
 # Taken from main Ubuntu Archive servers. Mostly for dealing with LFP.
 net.ipv4.tcp_congestion_control=bbr
+net.ipv4.tcp_notsent_lowat = 16384
 net.core.default_qdisc=fq
 
 
diff --git a/tests/unit/files/sysctl_net_tcp_congestion_control_bbr2.conf b/tests/unit/files/sysctl_net_tcp_congestion_control_bbr2.conf
index b3c31d7..562e554 100644
--- a/tests/unit/files/sysctl_net_tcp_congestion_control_bbr2.conf
+++ b/tests/unit/files/sysctl_net_tcp_congestion_control_bbr2.conf
@@ -1,5 +1,6 @@
 # Taken from main Ubuntu Archive servers. Mostly for dealing with LFP.
 net.ipv4.tcp_congestion_control=bbr2
+net.ipv4.tcp_notsent_lowat = 16384
 net.core.default_qdisc=fq
 
 
diff --git a/tests/unit/files/sysctl_net_tcp_congestion_control_no_bbr.conf b/tests/unit/files/sysctl_net_tcp_congestion_control_no_bbr.conf
index c043b68..4cf9e97 100644
--- a/tests/unit/files/sysctl_net_tcp_congestion_control_no_bbr.conf
+++ b/tests/unit/files/sysctl_net_tcp_congestion_control_no_bbr.conf
@@ -1,3 +1,4 @@
+net.ipv4.tcp_notsent_lowat = 16384
 net.core.default_qdisc=fq
 
 
diff --git a/tox.ini b/tox.ini
index 44e08eb..2e48886 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,7 +11,7 @@ setenv =
 [testenv:unit]
 commands = 
     pytest --ignore {toxinidir}/tests/functional \
-      {posargs:-v  --cov=lib --cov=reactive --cov=actions --cov-report=term-missing --cov-branch}
+      {posargs:-v  --cov=lib --cov=reactive --cov=actions --cov-branch --cov-report=term-missing --cov-report=html}
 deps = -r{toxinidir}/tests/unit/requirements.txt
        -r{toxinidir}/requirements.txt
 setenv =