A Decentralized failover and peer-to-peer node finding framework for Elixir. Using a TCP socket, Elixir nodes running Beethoven can find each other within a pre-defined network range.

Public API

• ready?/0 -> Returns true if Beethoven has fully initialized. False if not. Fully initialized is determined when the RoleMgmt Assigns server.

• until_ready/1 -> Holds the thread until Beethoven has fully initialized, or provided timeout value has become exhausted. Default timeout value is 5_000 milliseconds.

• get_node_status/0 -> Returns the status of the node within the Beethoven cluster. Possible returns are: :standalone & :clustered.

• get_cluster_nodes/0 -> Returns a list of all the nodes have have joined the Beethoven cluster.

• get_active_cluster_nodes/0 -> Similar to get_cluster_nodes/0, but only provides nodes that are active/online.

• get_detailed_cluster_nodes/0 -> Detailed list of all the nodes that have joined the Beethoven cluster + associated metadata.

• get_roles/0 -> Returns all Beethoven hosted roles with their associated metadata.

• whois_hosting/0 -> Looks up, and returns a list of nodes that host a given Beethoven role.

• allocate/0 -> Wrapper for Beethoven.Allocator.allocate/0.

Architecture

Beethoven is made of multiple smaller services that provide a depth of failover and loadbalancing functionality.

CoreServer

Monitors nodes in the Mnesia cluster. The server provides a behaviour that allows for PIDs to request a callback in the event of a node status change. The callback is called alert_me/0. This function is available to any module using CoreServer. Once used, the caller will be sent a GenServer cast containing the updated information.

{:node_update, {nodeName, status}}

Where status can be :offline or :online, and nodeName is the URI of the node. CoreServer manages the monitoring and de-monitoring nodes in Beethoven as they go through their lifecycle.

RoleMgmt

A framework for distributing work across a Beethoven cluster. Roles are defined in the :beethoven application configuration. These roles are hosted on the nodes that come into the cluster, and redistributed when they fail.

For more information on using RoleMgmt, please see the module's documentation.

Allocator

A signal based work allocator that helps determine how busy a given Beethoven cluster node is. Using these signals, it determines how busy a node is, and assigns a float. The smaller the float, the less busy a node is considered.

Using Beethoven.Allocator.Agent, you gain access to the signal() macro.

signal(name: :http_connections, weight: 10.0, type: :count)

This allows you to create your own signals to feed into the allocator. This method allows the allocator to be flexible, and signals to be declared and used as needed.

Calling Beethoven.Allocator.allocate/0 will check the Mnesia table used by the Allocator, and return the lest-busy node.

BeaconServer

This PID runs a TCP-Socket server to help new Beethoven nodes find each other. The port for listener can be set in the application configuration for Beethoven. Using this port, the Locator service within the other nodes can attempt to find each other.

This module utilizes Beethoven.SeekChat for (de)serialization of TCP calls.

Locator

This PID will enumerate all IPs within a given subnet; checking if they are running an instance of BeaconServer. This PID will enumerate the IPs 3 times. If nothing is found after the 3rd attempt, the cluster start as-is in :standalone mode.

This module utilizes Beethoven.SeekChat for (de)serialization of TCP calls.

HwMon

Set of PIDs to monitor and record historical hardware consumption. Will sample CPU and RAM usage every 5 seconds and save up to 100k samples per metric. When resources are sampled, a signal to Allocator is called and the utilization is logged.