create a prometheus exporter on a standard http port (#107)

* create a hyper server and add option to enable it in config

* move prometheus stuff to its own file; update format

* create metric type and help lookup table

* finish the metric help type map

* switch to a boolean and a standard port

* dont emit unimplemented metrics

* fail if curl returns a non 200

* resolve conflicts

* move log out of config.show and into main

* terminating new line

* upgrade curl

* include unimplemented stats

.circleci/config.yml

@@ -34,7 +34,7 @@ jobs:
           command: "cargo fmt --check"
       - run:
           name: "Install dependencies"
-          command: "sudo apt-get update && sudo apt-get install -y psmisc postgresql-contrib-12 postgresql-client-12 ruby ruby-dev libpq-dev python3 python3-pip lcov llvm-11"
+          command: "sudo apt-get update && sudo apt-get install -y psmisc postgresql-contrib-12 postgresql-client-12 ruby ruby-dev libpq-dev python3 python3-pip lcov llvm-11 && sudo apt-get upgrade curl"
       - run:
           name: "Install rust tools"
           command: "cargo install cargo-binutils rustfilt && rustup component add llvm-tools-preview"

.circleci/pgcat.toml

@@ -11,6 +11,9 @@ host = "0.0.0.0"
 # Port to run on, same as PgBouncer used in this example.
 port = 6432
 
+# enable prometheus exporter on port 9930
+enable_prometheus_exporter = true
+
 # How long to wait before aborting a server connection (ms).
 connect_timeout = 100
 

.circleci/run_tests.sh

@@ -31,6 +31,9 @@ toxiproxy-cli create -l 127.0.0.1:5433 -u 127.0.0.1:5432 postgres_replica
 
 start_pgcat "info"
 
+# Check that prometheus is running
+curl --fail localhost:9930/metrics
+
 export PGPASSWORD=sharding_user
 export PGDATABASE=sharded_db