Negotiate Docker API version (elastic#7165)

New Docker versions have deprecated our hardcoded client API version
(1.22), this change uses an API version negotiation mechanism to ensure
compatibility.

We should still upgrade to a newer client in the future, let's keep an
eye on moby/moby#33989 and do it once we have
something we can vendor.

CHANGELOG.asciidoc

@@ -62,6 +62,7 @@ https://github.com/elastic/beats/compare/v6.2.3...master[Check the HEAD diff]
 - Fix map overwrite panics by cloning shared structs before doing the update. {pull}6947[6947]
 - Fix error if lz4 compression is used with the kafka output. {pull}7025[7025]
 - Preserve the event when source matching fails in `add_docker_metadata`. {pull}7133[7133]
+- Negotiate Docker API version from our client instead of using a hardcoded one. {pull}7165[7165]
 
 *Auditbeat*
 

libbeat/common/docker/client.go

@@ -0,0 +1,44 @@
+package docker
+
+import (
+	"net/http"
+
+	"github.com/elastic/beats/libbeat/logp"
+
+	"github.com/docker/docker/api"
+	"github.com/docker/docker/api/types/versions"
+	"github.com/docker/docker/client"
+	"golang.org/x/net/context"
+)
+
+// Select Docker API version
+const dockerAPIVersion = api.DefaultVersion
+
+// NewClient builds and returns a new Docker client
+// It uses version 1.26 by default, and negotiates it with the server so it is downgraded if 1.26 is too high
+func NewClient(host string, httpClient *http.Client, httpHeaders map[string]string) (*client.Client, error) {
+	c, err := client.NewClient(host, dockerAPIVersion, httpClient, nil)
+	if err != nil {
+		return c, err
+	}
+
+	logp.Debug("docker", "Negotiating client version")
+	ping, err := c.Ping(context.Background())
+	if err != nil {
+		logp.Debug("docker", "Failed to perform ping: %s", err)
+	}
+
+	// try the latest version before versioning headers existed
+	if ping.APIVersion == "" {
+		ping.APIVersion = "1.24"
+	}
+
+	// if server version is lower than the client version, downgrade
+	if versions.LessThan(ping.APIVersion, dockerAPIVersion) {
+		c.UpdateClientVersion(ping.APIVersion)
+	}
+
+	logp.Debug("docker", "Client version set to %s", c.ClientVersion())
+
+	return c, nil
+}

libbeat/common/docker/watcher.go

@@ -9,7 +9,6 @@ import (
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/events"
 	"github.com/docker/docker/api/types/filters"
-	"github.com/docker/docker/client"
 	"github.com/docker/go-connections/tlsconfig"
 	"golang.org/x/net/context"
 
@@ -19,8 +18,7 @@ import (
 
 // Select Docker API version
 const (
-	dockerAPIVersion = "1.22"
-	shortIDLen       = 12
+	shortIDLen = 12
 )
 
 // Watcher reads docker events and keeps a list of known containers
@@ -106,7 +104,7 @@ func NewWatcher(host string, tls *TLSConfig, storeShortID bool) (Watcher, error)
 		}
 	}
 
-	client, err := client.NewClient(host, dockerAPIVersion, httpClient, nil)
+	client, err := NewClient(host, httpClient, nil)
 	if err != nil {
 		return nil, err
 	}

metricbeat/module/docker/docker.go

@@ -11,6 +11,7 @@ import (
 	"github.com/docker/docker/client"
 	"github.com/docker/go-connections/tlsconfig"
 
+	"github.com/elastic/beats/libbeat/common/docker"
 	"github.com/elastic/beats/metricbeat/mb"
 	"github.com/elastic/beats/metricbeat/mb/parse"
 )
@@ -67,7 +68,7 @@ func NewDockerClient(endpoint string, config Config) (*client.Client, error) {
 		}
 	}
 
-	client, err := client.NewClient(endpoint, dockerAPIVersion, httpClient, nil)
+	client, err := docker.NewClient(endpoint, httpClient, nil)
 	if err != nil {
 		return nil, err
 	}