Pipework

Software-Defined Networking for Linux Containers

Pipework lets you connect together containers in arbitrarily complex scenarios. Pipework uses cgroups and namespace and works with "plain" LXC containers (created with lxc-start), and with the awesome Docker.

Table of Contents

• Things to note
  • Virtualbox
  • Docker
• LAMP stack with a private network between the MySQL and Apache containers
• Docker integration
• Peeking inside the private network
• Setting container internal interface
• Using a different netmask
• Setting a default gateway
• Connect a container to a local physical interface
• Let the Docker host communicate over macvlan interfaces
• Wait for the network to be ready
• Add the interface without an IP address
• DHCP
• DHCP Options
• Specify a custom MAC address
• Virtual LAN (VLAN)
• Support Open vSwitch
• Support Infiniband
• Cleanup

### Things to note

Virtualbox

If you use VirtualBox, you will have to update your VM network settings. Open the settings panel for the VM, go the the "Network" tab, pull down the "Advanced" settings. Here, the "Adapter Type" should be pcnet (the full name is something like "PCnet-FAST III"), instead of the default e1000 (Intel PRO/1000). Also, "Promiscuous Mode" should be set to "Allow All". If you don't do that, bridged containers won't work, because the virtual NIC will filter out all packets with a different MAC address. If you are running VirtualBox in headless mode, the command line equivalent of the above is modifyvm --nicpromisc1 allow-all. If you are using Vagrant, you can add the following to the config for the same effect:

config.vm.provider "virtualbox" do |v|
  v.customize ['modifyvm', :id, '--nicpromisc1', 'allow-all']
end

Docker

Before using Pipework, please ask on the docker-user mailing list if there is a "native" way to achieve what you want to do without Pipework.

In the long run, Docker will allow complex scenarios, and Pipework should become obsolete.

If there is really no other way to plumb your containers together with the current version of Docker, then okay, let's see how we can help you!

The following examples show what Pipework can do for you and your containers.

### LAMP stack with a private network between the MySQL and Apache containers

Let's create two containers, running the web tier and the database tier:

APACHE=$(docker run -d apache /usr/sbin/httpd -D FOREGROUND)
MYSQL=$(docker run -d mysql /usr/sbin/mysqld_safe)

Now, bring superpowers to the web tier:

pipework br1 $APACHE 192.168.1.1/24

This will:

• create a bridge named br1 in the docker host;
• add an interface named eth1 to the $APACHE container;
• assign IP address 192.168.1.1 to this interface,
• connect said interface to br1.

Now (drum roll), let's do this:

pipework br1 $MYSQL 192.168.1.2/24

This will:

• not create a bridge named br1, since it already exists;
• add an interface named eth1 to the $MYSQL container;
• assign IP address 192.168.1.2 to this interface,
• connect said interface to br1.

Now, both containers can ping each other on the 192.168.1.0/24 subnet.

### Docker integration

Pipework can resolve Docker containers names. If the container ID that you gave to Pipework cannot be found, Pipework will try to resolve it with docker inspect. This makes it even simpler to use:

docker run -name web1 -d apache
pipework br1 web1 192.168.12.23/24

### Peeking inside the private network

Want to connect to those containers using their private addresses? Easy:

ip addr add 192.168.1.254/24 dev br1

Voilà!

### Setting container internal interface ## By default pipework creates a new interface `eth1` inside the container. In case you want to change this interface name like `eth2`, e.g., to have more than one interface set by pipework, use:

pipework br1 -i eth2 ...

Note:: for infiniband IPoIB interfaces, the default interface name is ib0 and not eth1.

### Using a different netmask

The IP addresses given to pipework are directly passed to the ip addr tool; so you can append a subnet size using traditional CIDR notation.

I.e.:

pipework br1 $CONTAINERID 192.168.4.25/20

Don't forget that all containers should use the same subnet size; pipework is not clever enough to use your specified subnet size for the first container, and retain it to use it for the other containers.

### Setting a default gateway

If you want outbound traffic (i.e. when the containers connects to the outside world) to go through the interface managed by Pipework, you need to change the default route of the container.

This can be useful in some usecases, like traffic shaping, or if you want the container to use a specific outbound IP address.

This can be automated by Pipework, by adding the gateway address after the IP address and subnet mask:

pipework br1 $CONTAINERID 192.168.4.25/20@192.168.4.1

### Connect a container to a local physical interface

Let's pretend that you want to run two Hipache instances, listening on real interfaces eth2 and eth3, using specific (public) IP addresses. Easy!

pipework eth2 $(docker run -d hipache /usr/sbin/hipache) 50.19.169.157/24
pipework eth3 $(docker run -d hipache /usr/sbin/hipache) 107.22.140.5/24

Note that this will use macvlan subinterfaces, so you can actually put multiple containers on the same physical interface.

### Let the Docker host communicate over macvlan interfaces

If you use macvlan interfaces as shown in the previous paragraph, you will notice that the host will not be able to reach the containers over their macvlan interfaces. This is because traffic going in and out of macvlan interfaces is segregated from the "root" interface.

If you want to enable that kind of communication, no problem: just create a macvlan interface in your host, and move the IP address from the "normal" interface to the macvlan interface.

For instance, on a machine where eth0 is the main interface, and has address 10.1.1.123/24, with gateway 10.1.1.254, you would do this:

ip addr del 10.1.1.123/24 dev eth0
ip link add link eth0 dev eth0m type macvlan mode bridge
ip link set eth0m up
ip addr add 10.1.1.123/24 dev eth0m
route add default gw 10.1.1.254

Then, you would start a container and assign it a macvlan interface the usual way:

CID=$(docker run -d ...)
pipework eth0 $CID 10.1.1.234/24@10.1.1.254

### Wait for the network to be ready

Sometimes, you want the extra network interface to be up and running before starting your service. A dirty (and unreliable) solution would be to add a sleep command before starting your service; but that could break in "interesting" ways if the server happens to be a bit slower at one point.

There is a better option: add the pipework script to your Docker image, and before starting the service, call pipework --wait. It will wait until the eth1 interface is present and in UP operational state, then exit gracefully.

If you need to wait on an interface other than eth1, pass the -i flag like this:

pipework --wait -i ib0

### Add the interface without an IP address

If for some reason you want to set the IP address from within the container, you can use 0/0 as the IP address. The interface will be created, connected to the network, and assigned to the container, but without configuring an IP address:

pipework br1 $CONTAINERID 0/0

### DHCP

You can use DHCP to obtain the IP address of the new interface. Just specify the name of the DHCP client that you want to use instead on an IP address; for instance:

pipework eth1 $CONTAINERID dhclient

You can specify the following DHCP clients:

• dhclient
• udhcpc
• dhcpcd
• dhcp

The first three are "normal" DHCP clients. They have to be installed on your host for this option to work. The last one works differently: it will run a DHCP client in a Docker container sharing its network namespace with your container. This allows to use DHCP configuration without worrying about installing the right DHCP client on your host. It will use the Docker busybox image and its embedded udhcpc client.

The value of $CONTAINERID will be provided to the DHCP client to use as the hostname in the DHCP request. Depending on the configuration of your network's DHCP server, this may enable other machines on the network to access the container using the $CONTAINERID as a hostname; therefore, specifying $CONTAINERID as a container name rather than a container id may be more appropriate in this use-case.

You need three things for this to work correctly:

• obviously, a DHCP server (in the example above, a DHCP server should be listening on the network to which we are connected on eth1);
• a DHCP client (either udhcpc, dhclient or dhcpcp) must be installed on your Docker host (you don't have to install it in your containers, but it must be present on the host), unless you specify dhcp as the client, in which case the Docker busybox image should be available;
• the underlying network must support bridged frames.

The last item might be particularly relevant if you are trying to bridge your containers with a WPA-protected WiFi network. I'm not 100% sure about this, but I think that the WiFi access point will drop frames originating from unknown MAC addresses; meaning that you have to go through extra hoops if you want it to work properly.

It works fine on plain old wired Ethernet, though.

### DHCP Options

You can specify extra DHCP options to be passed to the DHCP client by adding them with a semi-colon. For instance:

pipework eth1 $CONTAINERID dhcp:-f

This will tell Pipework to setup the interface using the DHCP client of the Docker busybox image, and pass -f as an extra flag to this DHCP client. This flag instructs the client to remain in the foreground instead of going to the background. Let's see what this means.

Without this flag, a new container is started, in which the DHCP client is executed. The DHCP client obtains a lease, then goes to the background. When it goes to the background, the PID 1 in this container exits, causing the whole container to be terminated. As a result, the "pipeworked" container has its IP address, but the DHCP client has gone. On the up side, you don't have any cleanup to do; on the other, the DHCP lease will not be renewed, which could be problematic if you have short leases and the server and other clients don't validate their leases before using them.

With this flag, a new container is started, it runs the DHCP client just like before; but when it obtains the lease, it remains in the foreground. As a result, the lease will be properly renewed. However, when you terminate the "pipeworked" container, you should also take care of removing the container that runs the DHCP client. This can be seen as an advantage if you want to reuse this network stack even if the initial container is terminated.

### Specify a custom MAC address

If you need to specify the MAC address to be used (either by the macvlan subinterface, or the veth interface), no problem. Just add it as the command-line, as the last argument:

pipework eth0 $(docker run -d haproxy) 192.168.1.2/24 26:2e:71:98:60:8f

This can be useful if your network environment requires whitelisting your hardware addresses (some hosting providers do that), or if you want to obtain a specific address from your DHCP server. Also, some projects like Orchestrator rely on static MAC-IPv6 bindings for DHCPv6:

pipework br0 $(docker run -d zerorpcworker) dhcp fa:de:b0:99:52:1c

Note: if you generate your own MAC addresses, try remember those two simple rules:

• the lowest bit of the first byte should be 0, otherwise, you are defining a multicast address;
• the second lowest bit of the first byte should be 1, otherwise, you are using a globally unique (OUI enforced) address.

In other words, if your MAC address is ?X:??:??:??:??:??, X should be 2, 6, a, or e. You can check Wikipedia if you want even more details.

Note: Setting the MAC address of an IPoIB interface is not supported.

Virtual LAN (VLAN)

If you want to attach the container to a specific VLAN, the VLAN ID can be specified using the [MAC]@VID notation in the MAC address parameter.

Note: VLAN attachment is currently only supported for containers to be attached to either an Open vSwitch bridge or a physical interface. Linux bridges are currently not supported.

The following will attach container zerorpcworker to the Open vSwitch bridge ovs0 and attach the container to VLAN ID 10.

pipework ovsbr0 $(docker run -d zerorpcworker) dhcp @10

### Support Open vSwitch

If you want to attach a container to the Open vSwitch bridge, no problem.

ovs-vsctl list-br
ovsbr0
pipework ovsbr0 $(docker run -d mysql /usr/sbin/mysqld_safe) 192.168.1.2/24

If the ovs bridge doesn't exist, it will be automatically created

### Support Infiniband IPoIB

Passing an IPoIB interface to a container is supported. However, the entire device is moved into the network namespace of the container. It therefore becomes hidden from the host.

To provide infiniband to multiple containers, use SR-IOV and pass the virtual function devices to the containers.

### Cleanup

When a container is terminated (the last process of the net namespace exits), the network interfaces are garbage collected. The interface in the container is automatically destroyed, and the interface in the docker host (part of the bridge) is then destroyed as well.