go.d docker respect DOCKER_HOST env var (#17979)

src/go/collectors/go.d.plugin/agent/discovery/sd/discoverer/dockerd/docker.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/netdata/netdata/go/go.d.plugin/agent/discovery/sd/model"
 	"github.com/netdata/netdata/go/go.d.plugin/logger"
+	"github.com/netdata/netdata/go/go.d.plugin/pkg/dockerhost"
 	"github.com/netdata/netdata/go/go.d.plugin/pkg/web"
 
 	"github.com/docker/docker/api/types"
@@ -43,6 +44,11 @@ func NewDiscoverer(cfg Config) (*Discoverer, error) {
 		started:        make(chan struct{}),
 	}
 
+	if addr := dockerhost.FromEnv(); addr != "" && d.addr == docker.DefaultDockerHost {
+		d.Infof("using docker host from environment: %s ", addr)
+		d.addr = addr
+	}
+
 	d.Tags().Merge(tags)
 
 	if cfg.Timeout.Duration().Seconds() != 0 {

src/go/collectors/go.d.plugin/modules/docker/docker.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/netdata/netdata/go/go.d.plugin/agent/module"
+	"github.com/netdata/netdata/go/go.d.plugin/pkg/dockerhost"
 	"github.com/netdata/netdata/go/go.d.plugin/pkg/web"
 
 	"github.com/docker/docker/api/types"
@@ -79,6 +80,10 @@ func (d *Docker) Configuration() any {
 }
 
 func (d *Docker) Init() error {
+	if addr := dockerhost.FromEnv(); addr != "" && d.Address == docker.DefaultDockerHost {
+		d.Infof("using docker host from environment: %s ", addr)
+		d.Address = addr
+	}
 	return nil
 }
 

src/go/collectors/go.d.plugin/pkg/dockerhost/dockerhost.go

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package dockerhost
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func FromEnv() string {
+	addr := os.Getenv("DOCKER_HOST")
+	if addr == "" {
+		return ""
+	}
+	if strings.HasPrefix(addr, "tcp://") || strings.HasPrefix(addr, "unix://") {
+		return addr
+	}
+	if strings.HasPrefix(addr, "/") {
+		return fmt.Sprintf("unix://%s", addr)
+	}
+	return fmt.Sprintf("tcp://%s", addr)
+}