client/cni: updated comments and simplified logic to auto download plugins

client/client.go

@@ -354,13 +354,14 @@ func NewClient(cfg *config.Config, consulCatalog consul.CatalogAPI, consulServic
 	c.configCopy = c.config.Copy()
 	c.configLock.Unlock()
 
+	// Auto download CNI binaries and configure CNI_PATH if requested.
 	if c.config.AutoFetchCNI {
-		cniGetter := NewCNIGetter(c.config.AutoFetchCNIURL, c.config.AutoFetchCNIDir)
-		c.logger.Info("downloading CNI plugins", "url", cniGetter.src)
-		if err := cniGetter.Get(); err != nil {
-			c.logger.Warn("failed to fetch CNI plugins", "url", cniGetter.src, "error", err)
-		} else {
-			c.config.CNIPath = cniGetter.CNIPath(c.config.CNIPath)
+		if cniPath := FetchCNIPlugins(c.logger, c.config.AutoFetchCNIURL, c.config.AutoFetchCNIDir); cniPath != "" {
+			if c.config.CNIPath == "" {
+				c.config.CNIPath = cniPath
+			} else {
+				c.config.CNIPath = c.config.CNIPath + ":" + cniPath
+			}
 			c.logger.Debug("using new CNI Path", "cni_path", c.config.CNIPath)
 		}
 	}
@@ -594,7 +595,7 @@ func (c *Client) init() error {
 	}
 
 	if c.config.AutoFetchCNI {
-		c.logger.Info("using alloc directory", "alloc_dir", c.config.AllocDir)
+		c.logger.Info("using cni directory for plugin downloads", "cni_dir", c.config.AutoFetchCNIDir)
 	}
 	return nil
 }

client/cni_autofetch.go

@@ -4,9 +4,9 @@ import (
 	"fmt"
 	"path/filepath"
 	"runtime"
-	"strings"
 
 	getter "github.com/hashicorp/go-getter"
+	hclog "github.com/hashicorp/go-hclog"
 )
 
 const (
@@ -14,38 +14,35 @@ const (
 )
 
 var (
+
+	// checksums are copied from https://github.com/containernetworking/plugins/releases
 	defaultCNIGetterChecksums = map[string]string{
 		"linux-amd64":   "sha256:e9bfc78acd3ae71be77eb8f3e890cc9078a33cc3797703b8ff2fc3077a232252",
 		"linux-arm":     "sha256:ae6ddbd87c05a79aceb92e1c8c32d11e302f6fc55045f87f6a3ea7e0268b2fda",
 		"linux-arm64":   "sha256:acde854e3def3c776c532ae521c19d8784534918cc56449ff16945a2909bff6d",
 		"windows-amd64": "sha256:a8a24e9cf93f4db92321afca3fe53bd3ccdf2b7117c403c55a5bac162d8d79cc",
 	}
-	defaultCNIGetterSrc = fmt.Sprintf("https://github.com/containernetworking/plugins/releases/download/v0.8.1/cni-plugins-%s-%s-v0.8.1.tgz?checksum=%s",
-		runtime.GOOS, runtime.GOARCH, defaultCNIGetterChecksums[runtime.GOOS+"-"+runtime.GOARCH])
+	defaultCNIPluginVersion = "0.8.1"
+	defaultCNIGetterSrc     = fmt.Sprintf("https://github.com/containernetworking/plugins/releases/download/v%s/cni-plugins-%s-%s-v%s.tgz?checksum=%s",
+		defaultCNIPluginVersion, runtime.GOOS, runtime.GOARCH, defaultCNIPluginVersion,
+		defaultCNIGetterChecksums[runtime.GOOS+"-"+runtime.GOARCH])
 )
 
-type CNIGetter struct {
-	src string
-	dst string
-}
-
-func NewCNIGetter(src, dataDir string) *CNIGetter {
+// FetchCNIPlugins downloads the standard set of CNI plugins to the client's
+// data directory and returns the path to be used when setting up the CNI_PATH
+// environment variable. If an error occures during download, it is logged and
+// an empty path is returned
+func FetchCNIPlugins(logger hclog.Logger, src string, dataDir string) string {
 	if src == "" {
 		src = defaultCNIGetterSrc
 	}
-	return &CNIGetter{
-		src: src,
-		dst: filepath.Join(dataDir, nomadCNIBinDir),
-	}
-}
 
-func (g *CNIGetter) Get() error {
-	return getter.Get(g.dst, g.src)
-}
-
-func (g *CNIGetter) CNIPath(path string) string {
-	if path == "" {
-		return g.dst
+	logger.Info("downloading CNI plugins", "url", src)
+	dst := filepath.Join(dataDir, nomadCNIBinDir)
+	if err := getter.Get(dst, src); err != nil {
+		logger.Warn("failed to fetch CNI plugins", "url", src, "error", err)
+		return ""
 	}
-	return path + ":" + g.dst
+
+	return dst
 }

command/agent/config.go

@@ -261,10 +261,14 @@ type ClientConfig struct {
 	// the host
 	BridgeNetworkSubnet string `hcl:"bridge_network_subnet"`
 
-	// AutoFetchCNIPlugins
-	AutoFetchCNIPlugins bool `hcl:"auto_fetch_cni_plugins`
+	// AutoFetchCNIPlugins toggles if the Nomad client should attempt to
+	// automatically download a standard set of CNI plugins, typically from
+	// the community repo https://github.com/containernetworking/plugins/releases
+	AutoFetchCNIPlugins bool `hcl:"auto_fetch_cni_plugins"`
 
-	// AutoFetchCNIPluginsURL
+	// AutoFetchCNIPluginsURL sets the source URL to be used if automatically
+	// downloading CNI plugins. If not set will use a known working version from
+	// the community repo https://github.com/containernetworking/plugins/releases
 	AutoFetchCNIPluginsURL string `hcl:"auto_fetch_cni_plugins_url"`
 }