Apache Mesos is an open source system for resource sharing across a cluster. It allows multiple frameworks to share a cluster by managing and scheduling resources. It is a cluster manager that provides isolation using Linux containers and allowing multiple systems such as Hadoop, Spark, Kafka, Storm, and more to share a cluster safely. It is highly scalable to thousands of nodes. It is a master/slave-based system and is fault tolerant, using Zookeeper for configuration management.

For a single master node Mesos cluster, the Spark master URL will be in this form:

mesos://<hostname>:5050.

Here, <hostname> is the hostname of the Mesos master server; the port is defined as 5050, which is the default Mesos master port (this is configurable). If there are multiple Mesos master servers in a large-scale high availability Mesos cluster, then the Spark master URL would look as follows:

mesos://zk://<hostname>:2181.

So, the election of the Mesos master server will be controlled by Zookeeper. The <hostname> will be the name of a host in the Zookeeper quorum. Also, the port number, 2181, is the default master port for Zookeeper.