Created a template configuration file and a tool that accepts command-line arguments to fill it out

release/mig-agent.cfg.template

@@ -0,0 +1,51 @@
+[agent]
+    ; connection string to the MIG relay. must contain credentials.
+    relay            = "{{.RelayAddress}}"
+
+    ; location of the mig api
+    api             = "{{.APIURL}}"
+
+    proxies         = "{{.Proxies}}"
+
+    ; location of the local stat socket
+    socket           = "127.0.0.1:{{.StatSocketPort}}"
+
+    ; frequency at which heartbeat messages are sent to the MIG relay
+    heartbeatfreq    = "120s"
+
+    ; timeout after which a module that has not finished is killed by the agent
+    moduletimeout    = "300s"
+
+    ; in immortal mode, the agent that encounter a fatal error
+    ; will attempt to restart itself instead of just shutting down
+    isimmortal       = {{.Immortal}}
+
+    ; installservice orders the agent to deploy a service init configuration
+    ; and start itself during the endpoint's boot process
+    installservice   = {{.InstallAsService}}
+
+    ; attempt to retrieve the public IP behind which the agent is running
+    discoverpublicip = on
+
+    ; in check-in mode, the agent connects to the relay, runs all pending commands
+    ; and exits. this mode is used to run the agent as a cron job, not a daemon.
+    checkin = {{.CronMode}}
+
+    refreshenv = "5m"
+
+    ; enable privacy mode
+    extraprivacymode = {{.ExtraPrivacy}}
+
+[stats]
+    maxactions = 15
+
+[certs]
+    ca  = "/etc/mig/ca.crt"
+    cert = "/etc/mig/agent.crt"
+    key = "/etc/mig/agent.key"
+
+[logging]
+    mode    = "file" ; stdout | file | syslog
+    level   = "debug"
+    file    = "/var/log/mig-agent.log"
+    maxfilesize = 10485760

tools/fill_mig_agent_cfg_template.go

@@ -0,0 +1,162 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path"
+	"strings"
+	"text/template"
+)
+
+const (
+	configTemplateDir  = "release"
+	configTemplateFile = "mig-agent.cfg.template"
+)
+
+// Defaults
+const (
+	defaultAPIURL           = "https://api.mig.mozilla.org/api/v1/"
+	defaultStatSocketPort   = 51664
+	defaultImmortal         = true
+	defaultInstallAsService = true
+	defaultCronMode         = false
+	defaultExtraPrivacy     = true
+)
+
+type proxyList []string
+
+// Config contains user-supplied configurable values that will be translated
+// and injected into `release/mig-agent.cfg.template` to produce a valid
+// `mig-agent.cfg`.
+type Config struct {
+	RelayAddress     string
+	APIURL           string
+	Proxies          proxyList
+	StatSocketPort   uint
+	Immortal         bool
+	InstallAsService bool
+	CronMode         bool
+	ExtraPrivacy     bool
+}
+
+// translatedConfig contains the same data as `Config` with some
+// transformations to make the output of this program consistent
+// with what mig agents expect.
+type translatedConfig struct {
+	RelayAddress     string
+	APIURL           string
+	Proxies          string
+	StatSocketPort   uint16
+	Immortal         string
+	InstallAsService string
+	CronMode         string
+	ExtraPrivacy     string
+}
+
+func onOrOff(on bool) string {
+	if on {
+		return "on"
+	} else {
+		return "off"
+	}
+}
+
+func translate(config Config) translatedConfig {
+	return translatedConfig{
+		RelayAddress:     config.RelayAddress,
+		APIURL:           config.APIURL,
+		Proxies:          strings.Join([]string(config.Proxies), ","),
+		StatSocketPort:   uint16(config.StatSocketPort),
+		Immortal:         onOrOff(config.Immortal),
+		InstallAsService: onOrOff(config.InstallAsService),
+		CronMode:         onOrOff(config.CronMode),
+		ExtraPrivacy:     onOrOff(config.ExtraPrivacy),
+	}
+}
+
+// IsValid verifies that values that must be supplied for a configuration have
+// been supplied and that those whose values cannot be guaranteed to be
+// correct by the type system and flag API are valid.
+func (config Config) IsValid() bool {
+	return config.RelayAddress != "" && config.StatSocketPort <= 65535
+}
+
+// String is required by the `flag.Value` interface.
+func (proxies *proxyList) String() string {
+	return strings.Join([]string(*proxies), ",")
+}
+
+// Set is required by the `flag.Value` interface. We use it to enable users to
+// supply multiple proxy addresses, which we collect into an array.
+func (proxies *proxyList) Set(value string) error {
+	*proxies = append(*proxies, value)
+	return nil
+}
+
+func main() {
+	templateFilePath := path.Join(configTemplateDir, configTemplateFile)
+	fmt.Fprintf(os.Stderr, "Trying to load template %s\n", templateFilePath)
+	template, err := template.ParseFiles(templateFilePath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error parsing template configuration: %s\n", err.Error())
+		os.Exit(1)
+	}
+
+	relayAddr := flag.String(
+		"relay",
+		"",
+		"Connection string to the MIG relay. Must contain credentials")
+	apiUrl := flag.String(
+		"api",
+		defaultAPIURL,
+		"URL of the MIG API")
+	var proxies proxyList
+	flag.Var(
+		&proxies,
+		"proxy",
+		"Address of a proxy to use. Multiple -proxy arguments are accepted")
+	statPort := flag.Uint(
+		"statport",
+		defaultStatSocketPort,
+		"Port to bind the agent's stat socket to on localhost")
+	immortal := flag.Bool(
+		"immortal",
+		defaultImmortal,
+		"Instruct the agent to automatically recover from fatal errors")
+	service := flag.Bool(
+		"service",
+		defaultInstallAsService,
+		"Instruct the agent to install itself as a service")
+	cronMode := flag.Bool(
+		"cron",
+		defaultCronMode,
+		"Instruct the agent to run all queued actions before terminating instead of running as a daemon")
+	extraPrivacy := flag.Bool(
+		"extraprivate",
+		defaultExtraPrivacy,
+		"Instruct the agent to run with extra privacy controls")
+	flag.Parse()
+
+	config := Config{
+		RelayAddress:     *relayAddr,
+		APIURL:           *apiUrl,
+		Proxies:          proxies,
+		StatSocketPort:   *statPort,
+		Immortal:         *immortal,
+		InstallAsService: *service,
+		CronMode:         *cronMode,
+		ExtraPrivacy:     *extraPrivacy,
+	}
+	if !config.IsValid() {
+		fmt.Fprintf(os.Stderr, "Invalid configuration data supplied. Check that the -relay argument is present and that the -statport argument is a valid port number.\n")
+		os.Exit(1)
+	}
+
+	translated := translate(config)
+	err = template.Execute(os.Stdout, translated)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error filling configuration template: %s\n", err.Error())
+		os.Exit(1)
+	}
+}