engine: add dnsmasq to engine config

This is needed so that llb.HTTP and llb.Git can respect custom DNS
config without relying on /etc/resolv.conf. Technically we're already
overriding /etc/resolv.conf, but something was causing Go to not attempt
to reload the config without a sleep(5 seconds).

Signed-off-by: Alex Suraci <alex@dagger.io>

cmd/engine/config.go

@@ -14,7 +14,7 @@ const engineDefaultShimBin = "/usr/local/bin/dagger-shim"
 // stack.
 const servicesDNSEnvName = "_EXPERIMENTAL_DAGGER_SERVICES_DNS"
 
-func setDaggerDefaults(cfg *config.Config, cniConfigPath string) error {
+func setDaggerDefaults(cfg *config.Config, netConf *networkConfig) error {
 	if cfg.Root == "" {
 		cfg.Root = engineDefaultStateDir
 	}
@@ -23,11 +23,21 @@ func setDaggerDefaults(cfg *config.Config, cniConfigPath string) error {
 		cfg.Workers.OCI.Binary = engineDefaultShimBin
 	}
 
-	if cniConfigPath != "" {
-		setNetworkDefaults(&cfg.Workers.OCI.NetworkConfig, cniConfigPath)
+	if cfg.DNS == nil {
+		cfg.DNS = &config.DNSConfig{}
+	}
+
+	// add dnsmasq as the default nameserver
+	cfg.DNS.Nameservers = append(
+		[]string{netConf.Bridge.String()},
+		cfg.DNS.Nameservers...,
+	)
+
+	if netConf.CNIConfigPath != "" {
+		setNetworkDefaults(&cfg.Workers.OCI.NetworkConfig, netConf.CNIConfigPath)
 
 		// we don't use containerd, but make it match anyway
-		setNetworkDefaults(&cfg.Workers.Containerd.NetworkConfig, cniConfigPath)
+		setNetworkDefaults(&cfg.Workers.Containerd.NetworkConfig, netConf.CNIConfigPath)
 	}
 
 	return nil

cmd/engine/main.go

@@ -241,7 +241,7 @@ func main() { //nolint:gocyclo
 		bklog.G(ctx).Debug("setting up engine networking")
 		networkContext, cancelNetworking := context.WithCancel(context.Background())
 		defer cancelNetworking()
-		cniConfigPath, err := setupNetwork(networkContext,
+		netConf, err := setupNetwork(networkContext,
 			c.GlobalString("network-name"),
 			c.GlobalString("network-cidr"),
 		)
@@ -250,7 +250,7 @@ func main() { //nolint:gocyclo
 		}
 
 		bklog.G(ctx).Debug("setting engine configs from defaults and flags")
-		if err := setDaggerDefaults(&cfg, cniConfigPath); err != nil {
+		if err := setDaggerDefaults(&cfg, netConf); err != nil {
 			return err
 		}
 
@@ -959,32 +959,46 @@ func (t *traceCollector) Export(ctx context.Context, req *tracev1.ExportTraceSer
 	return &tracev1.ExportTraceServiceResponse{}, nil
 }
 
-func setupNetwork(ctx context.Context, netName, netCIDR string) (string, error) {
+type networkConfig struct {
+	NetName       string
+	NetCIDR       string
+	Bridge        net.IP
+	CNIConfigPath string
+}
+
+func setupNetwork(ctx context.Context, netName, netCIDR string) (*networkConfig, error) {
 	if os.Getenv(servicesDNSEnvName) == "0" {
-		return "", nil
+		return nil, nil
 	}
 
 	bridge, err := network.BridgeFromCIDR(netCIDR)
 	if err != nil {
-		return "", fmt.Errorf("bridge from cidr: %w", err)
+		return nil, fmt.Errorf("bridge from cidr: %w", err)
 	}
 
+	// NB: this is needed for the Dagger shim worker at the moment for host alias
+	// resolution
 	err = network.InstallResolvconf(netName, bridge.String())
 	if err != nil {
-		return "", fmt.Errorf("install resolv.conf: %w", err)
+		return nil, fmt.Errorf("install resolv.conf: %w", err)
 	}
 
 	err = network.InstallDnsmasq(ctx, netName)
 	if err != nil {
-		return "", fmt.Errorf("install dnsmasq: %w", err)
+		return nil, fmt.Errorf("install dnsmasq: %w", err)
 	}
 
 	cniConfigPath, err := network.InstallCNIConfig(netName, netCIDR)
 	if err != nil {
-		return "", fmt.Errorf("install cni: %w", err)
+		return nil, fmt.Errorf("install cni: %w", err)
 	}
 
-	return cniConfigPath, nil
+	return &networkConfig{
+		NetName:       netName,
+		NetCIDR:       netCIDR,
+		Bridge:        bridge,
+		CNIConfigPath: cniConfigPath,
+	}, nil
 }
 
 type noopCacheImporter struct{}