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Project Name: MUSIC - Multi-site State Coordination Service

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To achieve 5 9s of availability on 3 9s or lower software and infrastructure in a cost-effective manner, ONAP components need to work in a reliable, active-active manner across multiple sites (platform-maturity resiliency level 3). A fundamental aspect of this is  statemanagement across geo-distributed sites in a reliable, scalable, highly available and efficient manner. This is an important and challenging problem because of three fundamental reasons:

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MUSIC also provides a rich set of recipes (mdbc, prom, musicCAS, musicQ) that ONAP components can use to build multi-site active-active/active-passive/federated state-management solutions:

• mdbc: The most crucial recipe is a multi-site database cache (mdbc) that enable ONAP components that maintain state in a SQLdatabase to avail the benefits of MUSIC without compromising their need to use transactional SQL DBs. These ONAP components can rely on existing db clustering techniques like MariaDB for transactionality and complex querying within a site. mdbc will intercept each of these read/write calls to the db cluster and mirror this state to other geo-distributed sites through MUSIC either synchronously or asynchronously (configurable at a table-level).  For example, components like the ONAP Service Orchestrator that use MariaDB to maintain state can directly use this recipe with no change to their SQL code.

• prom:  MUSIC provides a recipe for policy-driven ownership management (prom) of state for ONAP components to (1) partition state across replicas during both initial placement and during failures based on their individual policies (2) ensure correct transfer of state ownership across replicas during site failures and network partitions (3) ensure that the new owner has access to the most recent version of state (if needed).

• musicCAS: The distributed compare and set is a powerful primitive that will allow ONAP components to update shared state in  an atomic manner. This is currently being used by the ONAP HAS (homing service) that is structured a job scheduler with multiple workers trying to pick up client-submitted  jobs, while ensuring that only one of them actually performs the job.

• musicQ: Implementing a geo-distributed queue is a hard problem with many performance implications when data belonging to a queue is sharded across nodes. MUSIC provides a queue API that carefully structures the data to ensure good performance. ONAP HAS (mentioned above) uses this as its job queue.

Scope:

MUSIC is a shared service with recipes that individual ONAP components and micro-service can use for state replication, consistency management and state ownership across geo-management. While its intended granularity is at the ONAP component level, it will work well even for micro-services. For distributed sites. MUSIC will make sure that the right service data is available at the right place, and at the right time to enable federated active-active operation of ONAP. For example, we envisage the use of MUSIC for multi-site state management in SO (to store Camunda state across sites), <SDN-C, AppC> (to store ODL related state across sites) , A&AI (to store its graph data) and most other ONAP components that need to manage state across sites. 

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• MUSIC and its recipes have all been open sourced in github:MUSIC.

• Here is an overview of MUSIC's REST API: https://github.com/att/music/blob/master/RestMusicOverview.pdf

• MUSIC and mdbc together can support the following databases: Cassandra, MySQL, MariaDB, H2. 

• OOF-Homing Optimizer (HAS) uses MUSIC for its state persistence (as a queue) and as a highly available distributed messaging service. This is currently being run in production within ATT's ECOMP.

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