enhancement: Config override from flags (#121)

Allows overriding the config values defined in the file by values
supplied via the command line using the `--set` flag.

NOTICE.txt

@@ -90,3 +90,5 @@ go.uber.org/automaxprocs                                          Unknown
 go.uber.org/config                                                Unknown                                                                                          MIT
 go.uber.org/multierr                                              Unknown                                                                                          MIT
 go.uber.org/zap                                                   Unknown                                                                                          MIT
+helm.sh/helm/v3/pkg/strvals                                       Unknown                                                                                          Apache-2.0
+sigs.k8s.io/yaml                                                  Unknown                                                                                          MIT

cmd/server/server.go

@@ -4,13 +4,15 @@ package server
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"os/signal"
 
 	"github.com/google/gops/agent"
 	"github.com/spf13/cobra"
 	"go.uber.org/automaxprocs/maxprocs"
 	"go.uber.org/zap"
+	"helm.sh/helm/v3/pkg/strvals"
 
 	"github.com/cerbos/cerbos/internal/config"
 	"github.com/cerbos/cerbos/internal/observability/logging"
@@ -20,8 +22,9 @@ import (
 
 type serverArgs struct {
 	configFile      string
-	logLevel        string
+	configOverrides []string
 	debugListenAddr string
+	logLevel        string
 	zpagesEnabled   bool
 }
 
@@ -36,8 +39,9 @@ func NewCommand() *cobra.Command {
 	}
 
 	cmd.Flags().StringVar(&args.configFile, "config", "", "Path to config file")
-	cmd.Flags().StringVar(&args.logLevel, "log-level", "INFO", "Log level")
+	cmd.Flags().StringSliceVar(&args.configOverrides, "set", nil, "Config overrides")
 	cmd.Flags().StringVar(&args.debugListenAddr, "debug-listen-addr", "", "Address to start the gops listener")
+	cmd.Flags().StringVar(&args.logLevel, "log-level", "INFO", "Log level")
 	cmd.Flags().BoolVar(&args.zpagesEnabled, "zpages-enabled", false, "Enable zpages for debugging")
 
 	_ = cmd.Flags().MarkHidden("zpages-enabled")
@@ -66,8 +70,16 @@ func doRun(_ *cobra.Command, _ []string) error {
 	ctx, stopFunc := signal.NotifyContext(context.Background(), os.Interrupt)
 	defer stopFunc()
 
+	// load any config overrides
+	confOverrides := map[string]interface{}{}
+	for _, override := range args.configOverrides {
+		if err := strvals.ParseInto(override, confOverrides); err != nil {
+			return fmt.Errorf("failed to parse config override [%s]: %w", override, err)
+		}
+	}
+
 	// load configuration
-	if err := config.Load(args.configFile); err != nil {
+	if err := config.Load(args.configFile, confOverrides); err != nil {
 		return err
 	}
 

docs/modules/ROOT/pages/usage.adoc

@@ -4,12 +4,12 @@ include::partial$attributes.adoc[]
 
 == Starting the server
 
-The server is configured with a YAML file that is passed using the `--config` flag. See xref:configuration:index.adoc[Configuration] for more information about available configuration options.
+The server is configured with a YAML file that is passed using the `--config` flag. Values in the configuration file can be overridden from the command-line by the `--set` flag — which can be used multiple times. See xref:configuration:index.adoc[Configuration] for more information about available configuration options. 
 
 .Using the binary
 [source,sh,subs="attributes"]
 ----
-./{app-name} server --config=/path/to/config.yaml
+./{app-name} server --config=/path/to/config.yaml --set=server.httpListenAddr=:3592 
 ----
 
 .Using Docker
@@ -18,7 +18,7 @@ The server is configured with a YAML file that is passed using the `--config` fl
 docker run -i -t -p 3592:3592 \
     -v /path/to/conf/dir:/config \
     {app-docker-img} \
-    server --config=/config/conf.yaml
+    server --config=/config/conf.yaml --set=server.httpListenAddr=:3592
 ----
 
 == Compiling and testing policies

docs/modules/configuration/pages/index.adoc

@@ -3,7 +3,13 @@ include::ROOT:partial$attributes.adoc[]
 [[configuration]]
 = Configuration
 
-The Cerbos server is configured with a YAML file. Start the server by passing the configuration file using the `--config` flag. 
+The Cerbos server is configured with a YAML file. Start the server by passing the configuration file using the `--config` flag. The values defined in the file can be overridden from the command-line by using the `--set` flag. The `--set` flag can be used multiple times. For example, to override `server.httpListenAddr` and `engine.defaultPolicyVersion`, the `--set` flag can be used as follows:
+
+
+[source,sh,subs="attributes"]
+----
+./{app-name} server --config=/path/to/config.yaml --set=server.httpListenAddr=:3592 --set=engine.defaultPolicyVersion=staging
+----
 
 NOTE: Config values can reference environment variables by enclosing them between `${}`. E.g. `$$${HOME}$$`. 
 
@@ -17,6 +23,7 @@ server:
   grpcListenAddr: ":3593"
   metricsEnabled: true # Set to false to disable the /_cerbos/metrics endpoint
   logRequestPayloads: false # Set to true to log full request and response payloads. Affects performance.
+  playgroundEnabled: false # Set to true to enable the playground API.
   tls: # Optional
     cert: /path/to/certificate
     key: /path/to/private_key
@@ -37,7 +44,7 @@ storage:
   driver: "disk" # Valid values are "disk" or "git"
   disk: # Only required if "driver" is "disk"
     directory: pkg/test/testdata/store
-    readOnly: true 
+    watchForChanges: false 
   git: # Only required if the "driver" is "git"
     protocol: file # Valid values are "file", "ssh", "https"
     url: file://${HOME}/tmp/cerbos/policies 

go.mod

@@ -36,12 +36,10 @@ require (
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 // indirect
 	github.com/rivo/uniseg v0.2.0 // indirect
 	github.com/rjeczalik/notify v0.9.3-0.20201210012515-e2a77dcc14cf
-	github.com/rs/zerolog v1.20.0 // indirect
 	github.com/spf13/afero v1.6.0
 	github.com/spf13/cobra v1.1.3
 	github.com/stretchr/testify v1.7.0
 	github.com/tidwall/sjson v1.1.6
-	github.com/vektra/mockery/v2 v2.6.0
 	go.elastic.co/ecszap v1.0.0
 	go.opencensus.io v0.23.0
 	go.uber.org/automaxprocs v1.4.0
@@ -56,4 +54,9 @@ require (
 	google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.1.0
 	google.golang.org/protobuf v1.26.0
 	gotest.tools/gotestsum v1.6.4
+	helm.sh/helm/v3 v3.5.4
 )
+
+replace github.com/docker/distribution => github.com/docker/distribution v0.0.0-20191216044856-a8371794149d
+
+replace github.com/docker/docker => github.com/docker/docker v17.12.0-ce-rc1.0.20200618181300-9dc6525e6118+incompatible