[vtadmin] Add debug endpoints

[ajm188]

Description

This adds debug endpoints to vtadmin-api, namely the /debug/pprof/ friends, and also a /debug/env to show environment variables available to the vtadmin-api process.

net/http/pprof was being stubborn about how to get it to play nicely with gorilla/mux, but I managed to get it working, unfortunately at the cost of making the route registration a bit more confusing.

We also add some config options to opt users out of debug endpoints entirely, as well as to control the behavior of the /debug/env endpoint to sanitize, or omit entirely, any environment variables that may be sensitive.

Examples!

No changes to flags:

❯ curl -s localhost:14200/debug/env | grep CDPATH
CDPATH=:/Users/amason/work:/Users/amason/work

Adding sanitization:

diff --git a/examples/local/scripts/vtadmin-up.sh b/examples/local/scripts/vtadmin-up.sh
index e76a920618..4ceeee7b5d 100755
--- a/examples/local/scripts/vtadmin-up.sh
+++ b/examples/local/scripts/vtadmin-up.sh
@@ -9,6 +9,7 @@ vtadmin \
   --addr ":${vtadmin_api_port}" \
   --http-origin "http://localhost:3000" \
   --http-tablet-url-tmpl "http://{{ .Tablet.Hostname }}:15{{ .Tablet.Alias.Uid }}" \
+  --http-debug-sanitize-env "CDPATH" \
   --tracer "opentracing-jaeger" \
   --grpc-tracing \
   --http-tracing \

❯ curl -s localhost:14200/debug/env | grep CDPATH
CDPATH=********

Adding omission:

diff --git a/examples/local/scripts/vtadmin-up.sh b/examples/local/scripts/vtadmin-up.sh
index e76a920618..3172d4ddd6 100755
--- a/examples/local/scripts/vtadmin-up.sh
+++ b/examples/local/scripts/vtadmin-up.sh
@@ -9,6 +9,7 @@ vtadmin \
   --addr ":${vtadmin_api_port}" \
   --http-origin "http://localhost:3000" \
   --http-tablet-url-tmpl "http://{{ .Tablet.Hostname }}:15{{ .Tablet.Alias.Uid }}" \
+  --http-debug-omit-env "CDPATH" \
   --tracer "opentracing-jaeger" \
   --grpc-tracing \
   --http-tracing \

❯ curl -s localhost:14200/debug/env | grep -c CDPATH
0

Disabling entirely:

diff --git a/examples/local/scripts/vtadmin-up.sh b/examples/local/scripts/vtadmin-up.sh
index e76a920618..221006c4a4 100755
--- a/examples/local/scripts/vtadmin-up.sh
+++ b/examples/local/scripts/vtadmin-up.sh
@@ -9,6 +9,7 @@ vtadmin \
   --addr ":${vtadmin_api_port}" \
   --http-origin "http://localhost:3000" \
   --http-tablet-url-tmpl "http://{{ .Tablet.Hostname }}:15{{ .Tablet.Alias.Uid }}" \
+  --http-no-debug \
   --tracer "opentracing-jaeger" \
   --grpc-tracing \
   --http-tracing \

❯ curl localhost:14200/debug/env
404 page not found

I also poked around in the pprof endpoints and took some profiles.

Related Issue(s)

Closes #8267

Checklist

• Tests were added or are not required - n/a
• Documentation was added or is not required

Deployment Notes

[doeg]

I don't know much about pprof, but from a Go standpoint this looks great!

[doeg]

(Goodfellas voice) One's going left, the other's going right, so what?