We talked about the overall design of an online shopping store that can scale starting with our post here. Then we proceeded to discussing data infrastructure and data security in a system design case in previous posts. We started looking at a very specialized but increasingly popular analytics framework and Big Data to use with data sources. For example, Spark and Hadoop can be offered as a fully managed cloud offering. we continued looking at some more specialized infrastructure including dedicated private cloud. Then we added  serverless computing to the mix. Today we discuss marathon in detail. This is another specialization that is changing the typical landscape of application-database deployments in the traditional OLTP store.
Marathon is a container orchestration platform for Mesosphere's Datacenter Operating System (DC/OS) and Apache Mesos. Mesosphere is a platform for building data rich applications that can be portable across hybrid cloud. Mesos is a distributed systems kernel that unshackles us from a single box while providing us the same abstractions for CPU, Memory, Storage and other compute resources. It enables us with a fault-tolerant and elastic distributed systems. Together Marathon and Mesos provide a one-stop shop for an always-on always-connected, highly available, load-balanced, resource managed and cloud-portable deployment environment that is production ready.  Contrast this with the traditional dedicated resources in deployment environments in many enterprises and we see how managed the deployment environment has become. Moreover, it enables service discovery and load balancing so applications and services can be written as many as needed and configured with load balancer.  Anything that is hosted on Marathon automatically comes with health checks. Not only this we can also subscribe to events and collect metrics. The entire marathon framework is available via REST API for programmability. 
Perhaps the most interesting application is the hosting of database service on the Marathon containers. While load balancing for user services is a commonly understood practice, the same for a database service is lesser known. Marathon, however treats all services as code that can run on any container hosted on the same underlying distributed layer. The data persists on a shared volume and intra-cluster connectivity to the shared volume is trivial latency and redirection. That said storage and networking efficiency still needs to be carefully studied. Also, persistent volumes are used for applications to preserve they state because when they are restarted, they lose their state. A local volume that is pinned to the node will be available when that node relaunches. This bundles up the disk and the compute for that node.

#codingexercise
Find the first non-repeating character in a string
char GetNonRepeating(string str)
{
var h = new Hashtable();
for (int i = 0; i < str.Length; i++)
       if (h.Contains(str[i]))
           h[str[i]] += 1;
       else
           h.Add(str[i], 1);
char c= '\0';
for (int i = 0; i < str.Length; i++)
       if (h[str[i]] == 1) {
             c = str[i];
             break;
       }
return c;
}