Support passing env variables instead of flags (#31)

* Support passing env variables instead of flags

* Update readme to mention env vars

README.md

@@ -38,4 +38,43 @@ or using Docker as
 docker run -p 9042:9042 --rm datastax/cql-proxy:v0.0.1 --contact-points <cluster node IPs or DNS names>
 ```
 
+## Configuration
+
+To pass configuration to the cql-proxy both command line flags and environment variables can be used. Below are examples of
+the same command using both methods
+
+Flags
+
+```sh
+docker run -v <your-secure-connect-bundle.zip>:/tmp/scb.zip -p 9042:9042 --rm datastax/cql-proxy:v0.0.1 \
+--bundle /tmp/scb.zip --username token --password <your-astra-token>
+```
+
+Environment Variables
+
+```sh
+docker run -v <your-secure-connect-bundle.zip>:/tmp/scb.zip -p 9042:9042 --rm datastax/cql-proxy:v0.0.1 \
+-e BUNDLE=/tmp/scb.zip -e USERNAME=token -e PASSWORD=<your-astra-token>
+```
+
+To see what options are available the `-h` flag will display a help message listing all flags and their corresponding descriptions
+and environment variables
+
+```sh
+$ ./cql-proxy -h
+Usage: cql-proxy
+
+Flags:
+  -h, --help               Show context-sensitive help.
+  -b, --bundle=STRING      Path to secure connect bundle ($BUNDLE)
+  -u, --username=STRING    Username to use for authentication ($USERNAME)
+  -p, --password=STRING    Password to use for authentication ($PASSWORD)
+  -c, --contact-points=CONTACT-POINTS,...
+                           Contact points for cluster. Ignored if using the bundle path
+                           option ($CONTACT_POINTS).
+  -a, --bind=STRING        Address to use to bind serve ($BIND)
+      --debug              Show debug logging ($DEBUG)
+      --profiling          Enable profiling ($PROFILING)
+```
+
 [astra]: https://astra.datastax.com/

proxy.go

@@ -20,22 +20,23 @@ import (
 	"net/http"
 	_ "net/http/pprof"
 
-	"github.com/alecthomas/kong"
 	"cql-proxy/astra"
 	"cql-proxy/proxy"
 	"cql-proxy/proxycore"
+
+	"github.com/alecthomas/kong"
 	"github.com/datastax/go-cassandra-native-protocol/primitive"
 	"go.uber.org/zap"
 )
 
 var cli struct {
-	Bundle        string   `help:"Path to secure connect bundle" short:"b"`
-	Username      string   `help:"Username to use for authentication" short:"u"`
-	Password      string   `help:"Password to use for authentication" short:"p"`
-	ContactPoints []string `help:"Contact points for cluster. Ignored if using the bundle path option." short:"c"`
-	Bind          string   `help:"Address to use to bind serve" short:"a"`
-	Debug         bool     `help:"Show debug logging"`
-	Profiling     bool     `help:"Enable profiling"`
+	Bundle        string   `help:"Path to secure connect bundle" short:"b" env:"BUNDLE"`
+	Username      string   `help:"Username to use for authentication" short:"u" env:"USERNAME"`
+	Password      string   `help:"Password to use for authentication" short:"p" env:"PASSWORD"`
+	ContactPoints []string `help:"Contact points for cluster. Ignored if using the bundle path option." short:"c" env:"CONTACT_POINTS"`
+	Bind          string   `help:"Address to use to bind serve" short:"a" env:"BIND"`
+	Debug         bool     `help:"Show debug logging" env:"DEBUG"`
+	Profiling     bool     `help:"Enable profiling" env:"PROFILING"`
 }
 
 func main() {