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Lab 2.4 - Setup Mesos-DNS¶

If you want to be able to do service discovery with Mesos/Marathon, you need to install and setup mesos-dns.

To leverage marathon for scalability and HA, we will launch mesos-dns as an application from Marathon.

We will setup mesos-dns on mesos-agent1 (we will force mesos-dns to start on mesos-agent1 in Marathon - 10.2.10.22).

We need to do the following tasks:

Download the latest mesos-dns binaries
Configure mesos-dns
Launch the mesos-dns binary from Marathon

Download & Configure Mesos-DNS¶

SSH to mesos-agent1 and do the following:

curl -O -L https://github.com/mesosphere/mesos-dns/releases/download/v0.6.0/mesos-dns-v0.6.0-linux-amd64

mkdir /etc/mesos-dns

Create a file in /etc/mesos-dns/ called config.json and add the json block

vim /etc/mesos-dns/config.json

{
   "zk": "zk://10.2.10.21:2181/mesos",
   "masters": ["10.2.10.21:5050"],
   "refreshSeconds": 60,
   "ttl": 60,
   "domain": "mesos",
   "port": 53,
   "resolvers": ["8.8.8.8"],
   "timeout": 5,
   "httpon": true,
   "dnson": true,
   "httpport": 8123,
   "externalon": true,
   "SOAMname": "ns1.mesos",
   "SOARname": "root.ns1.mesos",
   "SOARefresh": 60,
   "SOARetry": 600,
   "SOAExpire": 86400,
   "SOAMinttl": 60,
   "IPSources": ["mesos", "host"]
}

Now setup the binary in a proper location:

mkdir /usr/local/mesos-dns

mv ./mesos-dns-v0.6.0-linux-amd64 /usr/local/mesos-dns/

chmod +x /usr/local/mesos-dns/mesos-dns-v0.6.0-linux-amd64

To test your setup do the following:

/usr/local/mesos-dns/mesos-dns-v0.6.0-linux-amd64 -config /etc/mesos-dns/config.json -v 10

This will start your mesos-dns app and you can test it.

You can now test your dns setup. Open a new command prompt from the windows jumpbox and start nslookup

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\user>nslookup
Default Server:  b.resolvers.Level3.net
Address:  4.2.2.2

> server 10.2.10.22
Default Server:  [10.2.10.22]
Address:  10.2.10.22

> www.google.com
Server:  [10.2.10.22]
Address:  10.2.10.22

Non-authoritative answer:
Name:    www.google.com
Addresses:  2607:f8b0:4007:80e::2004
         172.217.14.100

> master.mesos
Server:  [10.2.10.22]
Address:  10.2.10.22

Name:    master.mesos
Address:  10.2.10.21

>

Stop your test mesos-dns app by typing “CTRL-c”

Warning

The next steps will fail if you don’t stop your test mesos-dns app

Launch Mesos-DNS In Marathon¶

Launch the mesos-dns image in marathon. Connect to marathon, click on Create Application and enable JSON Mode. Copy the following JSON block over the default and click Create Application.

{
   "cmd": "/usr/local/mesos-dns/mesos-dns-v0.6.0-linux-amd64 -config=/etc/mesos-dns/config.json -v=10",
   "cpus": 0.2,
   "mem": 256,
   "id": "mesos-dns",
   "instances": 1,
   "constraints": [["hostname", "CLUSTER", "10.2.10.22"]]
}

Update /etc/resolv.conf on all agents by adding our mesos-dns nameserver to our /etc/resolv.conf file. SSH to mesos-agent1 & 2.
```
sed -i /nameserver/s/.*/"nameserver 10.2.10.22"/ /etc/resolv.conf
```

Note

If you have deployed your instances in a cloud like AWS, it is likely that you’ll lose your DNS setup after a reboot. If you want to make your changes persist, you need to update /etc/dhcp/dhclient.conf to supersede the dhcp setup. More information here: Static DNS server in a EC2 instance

Test Mesos-DNS¶

To test our Mesos DNS setup, we will start a new application and check if it automatically gets a DNS name.

Start a new app in marathon:

{
   "id": "app-test-dns",
   "cpus": 0.5,
   "mem": 32.0,
   "container": {
      "type": "DOCKER",
      "docker": {
         "image": "eboraas/apache-php",
         "network": "BRIDGE",
         "portMappings": [
            { "containerPort": 80, "hostPort": 0 }
         ]
      }
   }
}

Once it’s running, go to one of your slaves and run ping app-test-dns.marathon.mesos. It should work and return the agent IP.
If you don’t try to ping from mesos-agent1 or mesos-agent2, make sure your client can reach mesos-dns server first (10.2.10.22)

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