clusterchecks

README

Cluster check package

This package holds the cluster-agent logic to detect and dispatch cluster checks on node-agents that report to it. The actual scheduling as delegated to the node-agents' collector, the cluster-agent is only responsible for spreading the load across available nodes.

Architecture

                               +-------------+
                               | node agents |
                               +-+-----------+
                                 |
                                 | queries (/v1/api/clusterchecks/)
                                 |
                       +---------v----------+
+----------+  setups   |       Handler      |   watches   +----------------+
| AutoConf <-----------+     Public API     +-------------> leaderelection |
+-----+----+           |  init logic, glue  |             +----------------+
      |                +---------+----------+
      |                          |
      | sends                    | inits
      | configs                  | passes queries
      |                          |
      |            +-------------v-----------+
      |            |        dispatcher       |
      +------------>   Runs the dispatching  |
                   |   logic in a goroutine  |
                   |                         |
                   |   +-----------------+   |
                   |   |  clusterStore   |   |
                   |   | holds the state |   |
                   +---+-----------------+---+

Handler

The Handler class holds the init logic and the glue between components. It has the following scope:

• initialise the other classes and register them
• handle the api calls from the node-agents, through the dispatcher
• watch the leader-election status when configured, and handle the dispatcher's lifecycle accordingly

dispatcher

The dispatcher has the following scope:

• handle incoming messages (new / removed configs) from the AutoConf system, and update the store accordingly
• watch node statuses and de-register stale nodes
• re-dispatch orphaned configs
• expose its state to the Handler

clusterStore and nodeStore

These classes hold the dispatching state and provide convenience methods to make sure the state stays consistent. To ensure dispatcher operations (that require several reads / writes to the store) are atomic, the stores are designed with an external locking, held by the dispatcher on access.

Node-agent communication

The node-agent queries the cluster-agent through the autodiscovery ClusterChecksConfigProvider. As nodes can be removed without notice, the cluster-agent has to detect when a node is not connected anymore and re-dispatch the configurations to other, active, nodes.

This is handled by the node_expiration_timeout option (30 seconds by default) and the dispatcher.expireNodes method. The node-agents heartbeat is updated when they POST on the status url (10 seconds in the default configuration). When that heartbeat timestamp is too old, the node is deleted and its configurations put back in the dangling map.

Documentation

Index

• Variables
• func GetStats() (*types.Stats, error)
• type Handler
  • func NewHandler(_ autodiscovery.Component) (*Handler, error)
  • func (h *Handler) GetState() (types.StateResponse, error)
  • func (h *Handler) Run(_ context.Context) error

Variables

var (
	// ErrNotCompiled is returned if cluster check support is not compiled in.
	// User classes should handle that case as gracefully as possible.
	ErrNotCompiled = errors.New("cluster-check support not compiled in")
)

Functions

func GetStats

func GetStats() (*types.Stats, error)

GetStats not implemented

Types

type Handler

type Handler struct{}

Handler not implemented

func NewHandler

func NewHandler(_ autodiscovery.Component) (*Handler, error)

NewHandler not implemented

func (*Handler) GetState

func (h *Handler) GetState() (types.StateResponse, error)

GetState not implemented

func (*Handler) Run

func (h *Handler) Run(_ context.Context) error

Run not implemented