caddy-frontend: Allow to globally disable HTTP2

One of solutions for random 502 errors from caddy is to fully disable
HTTP2 protocol ( https://github.com/mholt/caddy/issues/1080 )

We run Caddy with HTTP2 enabled by default, as we can enable/disable it per
each slave, but in some environments it might be just better to fully avoid
HTTP2 codepaths in Caddy.

software/caddy-frontend/buildout.hash.cfg

@@ -14,7 +14,7 @@
 # not need these here).
 [template]
 filename = instance.cfg.in
-md5sum = d43a1631bcd0f4307507268a06f0fac2
+md5sum = de7e30546a952e306e2a74f8492ab419
 
 [template-common]
 filename = instance-common.cfg.in
@@ -22,7 +22,7 @@ md5sum = c801b7f9f11f0965677c22e6bbe9281b
 
 [template-apache-frontend]
 filename = instance-apache-frontend.cfg.in
-md5sum = db61a7c0aadba180b7aec6056d2c0019
+md5sum = 8b8fa3b9b080f14ca7ee2a010889a7dc
 
 [template-apache-replicate]
 filename = instance-apache-replicate.cfg.in

software/caddy-frontend/instance-apache-frontend.cfg.in

@@ -258,7 +258,9 @@ environment =
 command-line = {{ parameter_dict['caddy'] }}
   -conf ${dynamic-caddy-frontend-template:rendered}
   -log stdout
+{% if instance_parameter['configuration.global-disable-http2'].lower() not in TRUE_VALUES %}
   -http2=true
+{% endif %}
 {% if instance_parameter['configuration.enable-quic'].lower() in TRUE_VALUES %}
   -quic
 {% endif %}
@@ -716,7 +718,9 @@ environment =
 command-line = {{ parameter_dict['caddy'] }}
   -conf ${dynamic-nginx-frontend-template:rendered}
   -log stdout
+{% if instance_parameter['configuration.global-disable-http2'].lower() not in TRUE_VALUES %}
   -http2=true
+{% endif %}
   -grace {{ instance_parameter['configuration.mpm-graceful-shutdown-timeout'] }}s
   -disable-http-challenge
   -disable-tls-sni-challenge

software/caddy-frontend/instance-caddy-input-schema.json

@@ -45,6 +45,16 @@
       "title": "Enable HTTP2 by Default",
       "type": "string"
     },
+    "global-disable-http2": {
+      "default": "false",
+      "description": "Disables globally HTTP2 in Caddy, thus enable-http2-by-default here and enable-http2 have no effect. Rational is that in some loaded environments it is better to run Caddy without any HTTP2 capabilities.",
+      "enum": [
+        "true",
+        "false"
+      ],
+      "title": "Globally disable HTTP2",
+      "type": "string"
+    },
     "mpm-graceful-shutdown-timeout": {
       "default": 5,
       "description": "Value passed to -grace parameter of Caddy, see https://caddyserver.com/docs/cli .",

software/caddy-frontend/instance.cfg.in

@@ -97,6 +97,7 @@ configuration.trafficserver-autoconf-port = 8083
 configuration.trafficserver-mgmt-port = 8084
 configuration.re6st-verification-url = http://[2001:67c:1254:4::1]/index.html
 configuration.enable-http2-by-default = true
+configuration.global-disable-http2 = false
 configuration.enable-quic = false
 configuration.mpm-graceful-shutdown-timeout = 5
 configuration.monitor-httpd-port = 8072