Mesos DNS

This images contains the latest release of Mesos DNS (v0.4.0 as of 2015-10-12) on a minimal Alpine Linux base image. The overall size is just 27.5MB.

Configuration options

The following options can be passed to the Docker image:

• LOCAL_IP: The IP address the host has which should run Mesos DNS (mandatory, if your slave's hostname is not resolvable)
• MESOS_ZK: The ZooKeeper connection string for the Mesos Master(s), e.g. zk://192.168.0.100:2181/mesos (mandatory)
• MESOS_DNS_EXTERNAL_SERVERS: A comma-separated list of external DNS servers, e.g. 8.8.8.8,8.8.4.4 for the Google DNS servers. If not used, ``8.8.8.8` will be the default external DNS server.
• MESOS_DNS_HTTP_ENABLED: Whether the Mesos DNS web interface should be started. If not used or passed a true value, it will be disabled.
• MESOS_DNS_HTTP_PORT: The HTTP port of the Mesos DNS web interface. If not defined (and the web interface is enabled), 8123 will be used as port.
• MESOS_DNS_REFRESH: The frequency at which Mesos-DNS updates DNS records based on information retrieved from the Mesos master. The default value is 60 seconds.
• MESOS_DNS_TIMEOUT: The timeout threshold, in seconds, for connections and requests to external DNS requests. The default value is 5 seconds.

A further description of the Mesos DNS configuration parameters can be found on the reference docs.

DNS configuration on the host

As Mesos DNS needs an nameserver entry which points to the own host (the host which Mesos DNS is running on) in the /etc/resolv.conf at the begining of the file (see "Slave Setup"), it is necessary to prepare this entry before Mesos DNS can be run via Docker. The "pinning" of the image to a host is done via hostname constraints when running via Marathon.

Running

The image can be run either via Marathon (recommended!), or via command line on the Mesos Slave's Docker host.

Via Marathon

You should start the Mesos DNS per recommandation of the official docs via Marathon for each slave. This can be done via constraints in the application's JSON definition (see below). If you're running your Mesos Master/Slave as well as Marathon on IP address 192.168.0.100, a sample configuration would be the following:

curl -XPOST 'http://192.168.0.100:8080/v2/apps' -d '{
    "id": "mesos-dns-100",
    "env": {
        "LOCAL_IP": "192.168.0.100",
        "MESOS_ZK": "zk://192.168.0.100:2181/mesos",
        "MESOS_DNS_EXTERNAL_SERVERS": "8.8.8.8,8.8.4.4"
    },
    "container": {
        "docker": {
            "image": "tobilg/mesos-dns",
            "network": "HOST"
        },
        "type": "DOCKER"
    },
    "cpus": 0.2,
    "mem": 128,
    "instances": 1,
	"constraints": [["hostname", "CLUSTER", "192.168.0.100"]]
}'

Also, if you'd want to run Mesos DNS once on every slave available in the cluster, consider the following:

• Make sure that the slave's hostnames are resolvable via `nslookup ``hostname -f```)
• Set the instances property to the number of current Mesos slaves in the cluster

If everything is set, run this:

curl -XPOST 'http://192.168.0.100:8080/v2/apps' -d '{
    "id": "mesos-dns",
    "env": {
        "MESOS_ZK": "zk://192.168.0.100:2181/mesos",
        "MESOS_DNS_EXTERNAL_SERVERS": "8.8.8.8,8.8.4.4"
    },
    "container": {
        "docker": {
            "image": "tobilg/mesos-dns",
            "network": "HOST"
        },
        "type": "DOCKER"
    },
    "cpus": 0.2,
    "mem": 128,
    "instances": 1,
	"constraints": [["hostname", "UNIQUE"]]
}'

Via command line

docker run -d \
  --net=host \
  -e MESOS_ZK=zk://192.168.0.100:2181/mesos \
  -e LOCAL_IP=$(/sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}') \
  -e MESOS_DNS_EXTERNAL_SERVERS=8.8.8.8,8.8.4.4 \
  --name dns \
  -t tobilg/mesos-dns

Note: Use the correct network interface name, in our example it's eth0.