Docker Cookbook

7.11 Running Containers via Apache Mesos and Marathon | 219

---

To get started, clone the 
playa-mesos
repository from GitHub, start the virtual
machine via Vagrant, and 
ssh
to it:
$ git clone https://github.com/mesosphere/playa-mesos.git
$ vagrant up
$ vagrant ssh
Once the machine is up, you can access the Mesos web interface at 
http://
10.141.141.10:5050
 and the Marathon web interface at 
http://10.141.141.10:8080
.
Discussion on how to use 
Mesos
 and 
Marathon
are beyond the
scope of this book. Refer to the two websites for more information.
Marathon exposes a REST API that you can use to start tasks. Tasks are defined in a
JSON file and can be submitted to the API endpoint via 
curl
. Here is an example task
described in JSON:
{
"id"
:
"http"
,
"cmd"
:
"python -m SimpleHTTPServer $PORT0"
,
"mem"
:
50
,
"cpus"
:
0.1
,
"instances"
:
1
,
"constraints"
:
[
[
"hostname"
,
"UNIQUE"
]
],
"ports"
:
[
0
]
}
The 
id
is the name of the task (also called Application in Marathon). The 
cmd
is what
the application will run (here, a simple HTTP server via Python). What is important
to note is the use of 
ports
, which is set to a list containing 
0
. This means that Mara‐
thon will dynamically allocate a port that this application will use. This dynamic port
is passed to the 
cmd
argument as 
$PORT0
.
Save this JSON description in a file called 
test.json
and submit this application via
curl
:
$ curl -is -H "Content-Type: application/json"
-d @test.json 10.141.141.10:8080/v2/apps
HTTP/1.1 201 Created
...
Once the application starts, you will see it in the UI (
Figure 7-8
) and be able to access
the URL that points to the HTTP server that was just started. Note the port that was
dynamically allocated.