nomad-driver-containerd

  

Overview

Nomad task driver for launching containers using containerd.

Containerd (containerd.io) is a lightweight container daemon for running and managing container lifecycle.
Docker daemon also uses containerd.

dockerd (docker daemon) --> containerd --> containerd-shim --> runc

nomad-driver-containerd enables nomad client to launch containers directly using containerd, without docker!
Docker daemon is not required on the host system.

nomad-driver-containerd architecture

Requirements

• Nomad >=v0.11
• Go >=v1.11
• Containerd >=1.3
• Vagrant >=v2.2
• VirtualBox v6.0 (or any version vagrant is compatible with)

Building nomad-driver-containerd

Make sure your $GOPATH is setup correctly.

$ mkdir -p $GOPATH/src/github.com/Roblox
$ cd $GOPATH/src/github.com/Roblox
$ git clone git@github.com:Roblox/nomad-driver-containerd.git
$ cd nomad-driver-containerd
$ make build (This will build your containerd-driver binary)

Screencast

Wanna try it out!?

$ vagrant up

or vagrant provision if the vagrant VM is already running.

Once setup (vagrant up OR vagrant provision) is complete and the nomad server is up and running, you can check the registered task drivers (which will also show containerd-driver) using:

$ nomad node status (Note down the <node_id>)
$ nomad node status <node_id> | grep containerd-driver

NOTE: setup.sh is part of the vagrant setup and should not be executed directly.

Run Example jobs.

There are few example jobs in the example directory.

$ nomad job run <job_name.nomad>

will launch the job.

More detailed instructions are in the example README.md

Supported options

Driver Config

Option	Type	Required	Default	Description
enabled	bool	no	true	Enable/Disable task driver.
containerd_runtime	string	yes	N/A	Runtime for containerd e.g. io.containerd.runc.v1 or io.containerd.runc.v2.
stats_interval	string	no	1s	Interval for collecting TaskStats

Task Config

Option	Type	Required	Description
image	string	yes	OCI image (docker is also OCI compatible) for your container.
command	string	no	Command to override command defined in the image.
args	[]string	no	Arguments to the command.
cwd	string	no	Specify the current working directory for your container process. If the directory does not exist, one will be created for you.
privileged	bool	no	Run container in privileged mode. Your container will have all linux capabilities when running in privileged mode.
host_dns	bool	no	Default (true). By default, a container launched using containerd-driver will use host /etc/resolv.conf. This is similar to docker behavior. However, if you don't want to use host DNS, you can turn off this flag by setting host_dns=false.
seccomp	bool	no	Enable default seccomp profile. List of allowed syscalls.
seccomp_profile	string	no	Path to custom seccomp profile. seccomp must be set to true in order to use seccomp_profile. The default docker seccomp profile found here can be used as a reference, and modified to create a custom seccomp profile.
readonly_rootfs	bool	no	Container root filesystem will be read-only.
host_network	bool	no	Enable host network. This is equivalent to --net=host in docker.
cap_add	[]string	no	Add individual capabilities.
cap_drop	[]string	no	Drop invidual capabilities.
devices	[]string	no	A list of devices to be exposed to the container.
mounts	[]block	no	A list of mounts to be mounted in the container. Volume, bind and tmpfs type mounts are supported. fstab style mount options are supported.

Mount block
  {
   - type (string) (Optional): Supported values are volume, bind or tmpfs. Default: volume.
   - target (string) (Required): Target path in the container.
   - source (string) (Optional): Source path on the host.
   - options ([]string) (Optional): fstab style mount options. NOTE: For bind mounts, atleast rbind and ro are required.
  }

Bind mount example

mounts = [
           {
                type    = "bind"
                target  = "/target/t1"
                source  = "/src/s1"
                options = ["rbind", "ro"]
           }
        ]

Custom seccomp profile example

The default docker seccomp profile found here can be downloaded, and modified (by removing/adding syscalls) to create a custom seccomp profile.
The custom seccomp profile can then be saved under /opt/seccomp/seccomp.json on the Nomad client nodes.

A nomad job can be launched using this custom seccomp profile.

config {
	seccomp         = true
	seccomp_profile = "/opt/seccomp/seccomp.json"
}

Networking

nomad-driver-containerd supports host and bridge networks.

NOTE: host and bridge are mutually exclusive options, and only one of them should be used at a time.

1. Host network can be enabled by setting host_network to true in task config of the job spec (see under Supported options).

2. Bridge network can be enabled by setting the network stanza in the task group section of the job spec.

network {
  mode = "bridge"
}

You need to install CNI plugins on Nomad client nodes under /opt/cni/bin before you can use bridge networks.

Instructions for installing CNI plugins.

 $ curl -L -o cni-plugins.tgz https://github.com/containernetworking/plugins/releases/download/v0.8.6/cni-plugins-linux-amd64-v0.8.6.tgz
 $ sudo mkdir -p /opt/cni/bin
 $ sudo tar -C /opt/cni/bin -xzf cni-plugins.tgz

Also, ensure your Linux operating system distribution has been configured to allow container traffic through the bridge network to be routed via iptables. These tunables can be set as follows:

$ echo 1 > /proc/sys/net/bridge/bridge-nf-call-arptables
$ echo 1 > /proc/sys/net/bridge/bridge-nf-call-ip6tables
$ echo 1 > /proc/sys/net/bridge/bridge-nf-call-iptables

To preserve these settings on startup of a nomad client node, add a file including the following to /etc/sysctl.d/ or remove the file your Linux distribution puts in that directory.

net.bridge.bridge-nf-call-arptables = 1
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1

Port forwarding

nomad supports both static and dynamic port mapping.

1. Static ports

Static port mapping can be added in the network stanza.

network {
  mode = "bridge"
  port "lb" {
    static = 8889
    to     = 8889
  }
}

Here, host port 8889 is mapped to container port 8889.
NOTE: static ports are usually not recommended, except for system or specialized jobs like load balancers.

2. Dynamic ports

Dynamic port mapping is also enabled in the network stanza.

network {
  mode = "bridge"
  port "http" {
    to = 8080
  }
}

Here, nomad will allocate a dynamic port on the host and that port will be mapped to 8080 in the container.

You can also read more about network stanza in the nomad official documentation

Service discovery

Nomad schedules workloads of various types across a cluster of generic hosts. Because of this, placement is not known in advance and you will need to use service discovery to connect tasks to other services deployed across your cluster. Nomad integrates with Consul to provide service discovery and monitoring.

A service stanza can be added to your job spec, to enable service discovery.

The service stanza instructs Nomad to register a service with Consul.

Tests

$ make test

NOTE: These are destructive tests and can leave the system in a changed state.
It is highly recommended to run these tests either as part of a CI/CD system or on a immutable infrastructure e.g VMs.

Cleanup

make clean

This will delete your binary: containerd-driver

vagrant destroy

This will destroy your vagrant VM.

Currently supported environments

Ubuntu (>= 16.04)

License

Copyright 2020 Roblox Corporation

Licensed under the Apache License, Version 2.0 (the "License"). For more information read the License.