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• Node Managers that register with the Resource Manager with (0 memory, 0 CPU) are eligible for fine-grained scaling, that is, Myriad expands and shrinks the capacity of the Node Managers with the resources offered by Mesos. Further, Myriad ensures that YARN containers are launched on the Node Managers only if Mesos offers enough resources on the slave nodes running those Node Managers.
• A zero profile is defined in the Myriad configuration file, myriad-config-default.yml, to help administrators launch Node Managers with (0 memory, 0 CPU) capacities using the Myriad Cluster APIvia the REST /api/cluster/flexup command).
• Node Managers that register with Resource with the Resource Manager with more than (0 memory, 0 CPU) are not eligible for fine-grained scaling. For example, Myriad will does not expand and shrink the capacity of the Node Managers. These Node Node Managers are typically launched with a low, medium, or high profile.

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The administrator launches Node Managers with zero capacity (via the REST /api/cluster/flexup command) . The Node and theNode Managers report zero capacity to the Resource Manager upon registration.

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1. The application is added to the Resource Manager's scheduling pipeline.
   
   • If a Node Manager has a zero profile, the YARN scheduler (for example. FairShareScheduler) does not allocate any application containers.
   • If a Node Manager has a non-zero capacity (low, medium, or high profiles), containers might be allocated for those Node Managers depending on their free capacity.
2. Myriad receives resource offers from Mesos for slave nodes running zero profile Node Managers.
3. The offered resources are projected to YARN's scheduler as available capacity of the zero profile Node Manager. For example, if Mesos offers (10G memory, 4CPU) for a given node, then the capacity of the zero profile Node Managers running on that node increases to (10G memory, 4 CPU).
4. The YARN scheduler allocates a few containers for the zero profile Node Managers.
5. • For each allocated container, Myriad spins up a placeholder Mesos task that holds on to Mesos resources as long as the corresponding YARN container is alive. The placeholder tasks are launched in a single shot, corresponding to the containers that YARN allocates.
   • Node Managers become aware of container allocations via YARN's HBase mechanism.
   • Myriad ensures that Node Managers are made aware of container allocations only after the corresponding placeholder Mesos tasks are launched.
6. When Node When the Node Managers report to Resource to the Resource Manager that some of the containers have finished, Myriad sends out finished status updates to Mesos for the corresponding placeholder tasks.
7. Mesos takes back the resources from Myriad that were held using placeholder tasks upon receiving the after receiving a finished status updatesupdate.

Trying out Fine-grained Scaling

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