support reading systemctl config automatically on baremetal setups (#15066)

this allows for customers to use `mc admin service restart`
directly even when performing RPM, DEB upgrades. Upon such 'restart'
after upgrade MinIO will re-read the /etc/default/minio for any
newer environment variables.

As long as `MINIO_CONFIG_ENV_FILE=/etc/default/minio` is set, this
is honored.

README.md

@@ -236,16 +236,16 @@ Upgrades require zero downtime in MinIO, all upgrades are non-disruptive, all tr
 mc admin update <minio alias, e.g., myminio>
 ```
 
-- For deployments without external internet access (e.g. airgapped environments), download the binary from <https://dl.min.io> and replace the existing MinIO binary let's say for example `/opt/bin/minio`, apply executable permissions `chmod +x /opt/bin/minio` and do `mc admin service restart alias/`.
+- For deployments without external internet access (e.g. airgapped environments), download the binary from <https://dl.min.io> and replace the existing MinIO binary let's say for example `/opt/bin/minio`, apply executable permissions `chmod +x /opt/bin/minio` and proceed to perform `mc admin service restart alias/`.
 
-- For installations using Systemd MinIO service, upgrade via RPM/DEB packages **parallelly** on all servers or replace the binary lets say `/opt/bin/minio` on all nodes, apply executable permissions `chmod +x /opt/bin/minio`. Proceed to perform `systemctl restart minio` across all nodes in **parallel**.
+- For installations using Systemd MinIO service, upgrade via RPM/DEB packages **parallelly** on all servers or replace the binary lets say `/opt/bin/minio` on all nodes, apply executable permissions `chmod +x /opt/bin/minio` and process to perform `mc admin service restart alias/`.
 
 ### Upgrade Checklist
 
 - Test all upgrades in a lower environment (DEV, QA, UAT) before applying to production. Performing blind upgrades in production environments carries significant risk.
-- Read the release notes for the targeted MinIO release *before* performing any installation, there is no forced requirement to upgrade to latest releases every week. If it has a bug fix you are looking for then yes, else avoid actively upgrading a running production system.
+- Read the release notes for MinIO *before* performing any upgrade, there is no forced requirement to upgrade to latest releases upon every releases. Some releases may not be relevant to your setup, avoid upgrading production environments unnecessarily.
-- If you plan to use `mc admin update`, MinIO process must have write access to the parent directory to provide in-place upgrades.
+- If you plan to use `mc admin update`, MinIO process must have write access to the parent directory where the binary is present on the host system.
-- `mc admin update` is not supported in kubernetes/container environments, container environments provide their own mechanisms for container updates.
+- `mc admin update` is not supported and should be avoided in kubernetes/container environments, please upgrade containers by upgrading relevant container images.
 - **We do not recommend upgrading one MinIO server at a time, the product is designed to support parallel upgrades please follow our recommended guidelines.**
 
 ## Explore Further

cmd/common-main.go

@@ -526,9 +526,6 @@ func parsEnvEntry(envEntry string) (envKV, error) {
 func minioEnvironFromFile(envConfigFile string) ([]envKV, error) {
 	f, err := os.Open(envConfigFile)
 	if err != nil {
-		if os.IsNotExist(err) { // ignore if file doesn't exist.
-			return nil, nil
-		}
 		return nil, err
 	}
 	defer f.Close()
@@ -624,7 +621,7 @@ func loadEnvVarsFromFiles() {
 
 	if env.IsSet(config.EnvConfigEnvFile) {
 		ekvs, err := minioEnvironFromFile(env.Get(config.EnvConfigEnvFile, ""))
-		if err != nil {
+		if err != nil && !os.IsNotExist(err) {
 			logger.Fatal(err, "Unable to read the config environment file")
 		}
 		for _, ekv := range ekvs {

cmd/server-main.go

@@ -138,6 +138,13 @@ func serverCmdArgs(ctx *cli.Context) []string {
 		logger.FatalIf(err, "Unable to validate passed arguments in %s:%s",
 			config.EnvArgs, os.Getenv(config.EnvArgs))
 	}
+	if v == "" {
+		v, _, _, err = env.LookupEnv(config.EnvVolumes)
+		if err != nil {
+			logger.FatalIf(err, "Unable to validate passed arguments in %s:%s",
+				config.EnvVolumes, os.Getenv(config.EnvVolumes))
+		}
+	}
 	if v == "" {
 		// Fall back to older environment value MINIO_ENDPOINTS
 		v, _, _, err = env.LookupEnv(config.EnvEndpoints)
@@ -422,12 +429,12 @@ func serverMain(ctx *cli.Context) {
 	erasureSelfTest()
 	compressSelfTest()
 
-	// Handle all server command args.
-	serverHandleCmdArgs(ctx)
-
 	// Handle all server environment vars.
 	serverHandleEnvVars()
 
+	// Handle all server command args.
+	serverHandleCmdArgs(ctx)
+
 	// Set node name, only set for distributed setup.
 	globalConsoleSys.SetNodeName(globalLocalNodeName)
 

internal/config/constants.go

@@ -48,6 +48,7 @@ const (
 	EnvPublicIPs  = "MINIO_PUBLIC_IPS"
 	EnvFSOSync    = "MINIO_FS_OSYNC"
 	EnvArgs       = "MINIO_ARGS"
+	EnvVolumes    = "MINIO_VOLUMES"
 	EnvDNSWebhook = "MINIO_DNS_WEBHOOK_ENDPOINT"
 
 	EnvSiteName   = "MINIO_SITE_NAME"