Add support to disable creation of network config files

Specifically, we want to be able to specify whether resolv.conf
and /etc/hosts will be create and bind-mounted into the
container.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/container.go

@@ -293,6 +293,10 @@ type ContainerConfig struct {
 	// namespace
 	// These are not used unless CreateNetNS is true
 	PortMappings []ocicni.PortMapping `json:"portMappings,omitempty"`
+	// NoCreateResolvConf indicates that resolv.conf should not be
+	// bind-mounted inside the container.
+	// Conflicts with DNSServer, DNSSearch, DNSOption.
+	NoCreateResolvConf bool
 	// DNS servers to use in container resolv.conf
 	// Will override servers in host resolv if set
 	DNSServer []net.IP `json:"dnsServer,omitempty"`
@@ -302,6 +306,10 @@ type ContainerConfig struct {
 	// DNS options to be set in container resolv.conf
 	// With override options in host resolv if set
 	DNSOption []string `json:"dnsOption,omitempty"`
+	// NoCreateHosts indicates that /etc/hosts should not be
+	// bind-mounted inside the container.
+	// Conflicts with HostAdd.
+	NoCreateHosts bool
 	// Hosts to add in container
 	// Will be appended to host's host file
 	HostAdd []string `json:"hostsAdd,omitempty"`

libpod/container_internal_linux.go

@@ -703,10 +703,11 @@ func (c *Container) makeBindMounts() error {
 			}
 		}
 
-		if c.config.NetNsCtr != "" {
+		if c.config.NetNsCtr != "" && (!c.config.NoCreateHosts || !c.config.NoCreateResolvConf) {
-			// We share a net namespace
+			// We share a net namespace.
 			// We want /etc/resolv.conf and /etc/hosts from the
-			// other container
+			// other container. Unless we're not creating both of
+			// them.
 			depCtr, err := c.runtime.state.Container(c.config.NetNsCtr)
 			if err != nil {
 				return errors.Wrapf(err, "error fetching dependency %s of container %s", c.config.NetNsCtr, c.ID())
@@ -718,13 +719,16 @@ func (c *Container) makeBindMounts() error {
 				return errors.Wrapf(err, "error fetching bind mounts from dependency %s of container %s", depCtr.ID(), c.ID())
 			}
 
+			if !c.config.NoCreateResolvConf {
 				// The other container may not have a resolv.conf or /etc/hosts
 				// If it doesn't, don't copy them
 				resolvPath, exists := bindMounts["/etc/resolv.conf"]
 				if exists {
 					c.state.BindMounts["/etc/resolv.conf"] = resolvPath
 				}
+			}
 
+			if !c.config.NoCreateHosts {
 				// check if dependency container has an /etc/hosts file
 				hostsPath, exists := bindMounts["/etc/hosts"]
 				if !exists {
@@ -745,28 +749,37 @@ func (c *Container) makeBindMounts() error {
 
 				// finally, save it in the new container
 				c.state.BindMounts["/etc/hosts"] = hostsPath
+			}
 		} else {
+			if !c.config.NoCreateResolvConf {
 				newResolv, err := c.generateResolvConf()
 				if err != nil {
 					return errors.Wrapf(err, "error creating resolv.conf for container %s", c.ID())
 				}
 				c.state.BindMounts["/etc/resolv.conf"] = newResolv
+			}
 
+			if !c.config.NoCreateHosts {
 				newHosts, err := c.generateHosts("/etc/hosts")
 				if err != nil {
 					return errors.Wrapf(err, "error creating hosts file for container %s", c.ID())
 				}
 				c.state.BindMounts["/etc/hosts"] = newHosts
 			}
+		}
 
+		if c.state.BindMounts["/etc/hosts"] != "" {
 			if err := label.Relabel(c.state.BindMounts["/etc/hosts"], c.config.MountLabel, true); err != nil {
 				return err
 			}
+		}
 
+		if c.state.BindMounts["/etc/resolv.conf"] != "" {
 			if err := label.Relabel(c.state.BindMounts["/etc/resolv.conf"], c.config.MountLabel, true); err != nil {
 				return err
 			}
 		}
+	}
 
 	// SHM is always added when we mount the container
 	c.state.BindMounts["/dev/shm"] = c.config.ShmDir

libpod/options.go

@@ -997,6 +997,9 @@ func WithDNSSearch(searchDomains []string) CtrCreateOption {
 		if ctr.valid {
 			return ErrCtrFinalized
 		}
+		if ctr.config.NoCreateResolvConf {
+			return errors.Wrapf(ErrInvalidArg, "cannot add DNS search domains if container will not create /etc/resolv.conf")
+		}
 		ctr.config.DNSSearch = searchDomains
 		return nil
 	}
@@ -1008,6 +1011,9 @@ func WithDNS(dnsServers []string) CtrCreateOption {
 		if ctr.valid {
 			return ErrCtrFinalized
 		}
+		if ctr.config.NoCreateResolvConf {
+			return errors.Wrapf(ErrInvalidArg, "cannot add DNS servers if container will not create /etc/resolv.conf")
+		}
 		var dns []net.IP
 		for _, i := range dnsServers {
 			result := net.ParseIP(i)
@@ -1027,6 +1033,9 @@ func WithDNSOption(dnsOptions []string) CtrCreateOption {
 		if ctr.valid {
 			return ErrCtrFinalized
 		}
+		if ctr.config.NoCreateResolvConf {
+			return errors.Wrapf(ErrInvalidArg, "cannot add DNS options if container will not create /etc/resolv.conf")
+		}
 		ctr.config.DNSOption = dnsOptions
 		return nil
 	}
@@ -1038,6 +1047,11 @@ func WithHosts(hosts []string) CtrCreateOption {
 		if ctr.valid {
 			return ErrCtrFinalized
 		}
+
+		if ctr.config.NoCreateHosts {
+			return errors.Wrapf(ErrInvalidArg, "cannot add hosts if container will not create /etc/hosts")
+		}
+
 		ctr.config.HostAdd = hosts
 		return nil
 	}
@@ -1184,6 +1198,44 @@ func WithCtrNamespace(ns string) CtrCreateOption {
 	}
 }
 
+// WithNoCreateResolvConf tells the container not to bind-mount resolv.conf in.
+// This conflicts with other DNS-related options.
+func WithNoCreateResolvConf() CtrCreateOption {
+	return func(ctr *Container) error {
+		if ctr.valid {
+			return ErrCtrFinalized
+		}
+
+		if len(ctr.config.DNSServer) != 0 ||
+			len(ctr.config.DNSSearch) != 0 ||
+			len(ctr.config.DNSOption) != 0 {
+			return errors.Wrapf(ErrInvalidArg, "not creating resolv.conf conflicts with DNS options")
+		}
+
+		ctr.config.NoCreateResolvConf = true
+
+		return nil
+	}
+}
+
+// WithNoCreateHosts tells the container not to bind-mount /etc/hosts in.
+// This conflicts with WithHosts().
+func WithNoCreateHosts() CtrCreateOption {
+	return func(ctr *Container) error {
+		if ctr.valid {
+			return ErrCtrFinalized
+		}
+
+		if len(ctr.config.HostAdd) != 0 {
+			return errors.Wrapf(ErrInvalidArg, "not creating /etc/hosts conflicts with adding to the hosts file")
+		}
+
+		ctr.config.NoCreateHosts = true
+
+		return nil
+	}
+}
+
 // withIsInfra sets the container to be an infra container. This means the container will be sometimes hidden
 // and expected to be the first container in the pod.
 func withIsInfra() CtrCreateOption {