CONSULConsul at a glance.

!The microservices architecture service discovery engine

!Enabling reactive programming by providing a reliable list of nodes participating in a cluster

Consul provides a consistent view of services and configuration

CONSUL

• Service Discovery

• Health

• Config

Consul uses a microservices architecture to provide reliable service discovery and health monitoring

CONSUL• Consul provides service discovery

• Consul provides a consistent view of services

• Consul provides a consistent view of configuration

• Consul uses a microservice interface to a replicated view of your topology and its configuration

• Consul can monitor and change services topology based on health

FEATURES• scalable distributed health checks

• minimal dc to dc communication

• event system

• domain model for managing topology of datacenters, server nodes, and services running on server nodes along with their configuration

CONSUL LIKE

• DNS server plus Consistent Key/Value Store + ZooKeeper + Nagios + … = Consul

• All the bits you need in a coherent model available to provide service discovery and replicated config

UI

SERVICES IN CATALOG• available via DNS

• available via REST interface

• Consul is a microservice architecture

• HTTP

• JSON

AGENT• Long running daemon on every member of Consul

cluster

• Client or server mode

• Client runs on server hosting services

• All nodes run an agent

• Stays in sync, interface with REST and DHCP

CLIENT

• Agent that forwards request to server

• Mostly stateless

• Client does LAN gossip (low traffic)

SERVER• Server also agent with more tasks

• RAFT quorum, who is leader/master

• Maintain cluster state

• Handles WAN gossip to other datacenters

• Forwards queries to leader/master

• Forward queries to other datacenters

DATACENTER

• Datacenter - obvious?

• EC2 availability zone

• Networking environment

• Private, low latency, and high bandwidth

• Fast between nodes, no hops, little routing, high speed

CONSENSUS• Agreement on who is the leader

• Transactional finite state machine

• Replicated Log, FSM, Peer Set (who gets the replicated log), Quorum (majority of peers agree), Committed Entry, Leader

• End Result: Consistent view of configuration and live services

GOSSIP

• Consul is built on top of Serf,

• Serf is a full gossip protocol

• Serf provides membership, failure detection, and event broadcast mechanisms

• Clustering of server nodes

LAN, WAN, AND RPC• LAN Gossip -

• LAN gossip pool,

• all agent nodes (client and server) on same local network or datacenter

• WAN Gossip -

• WAN gossip pool

• Only agent servers

• Servers per datacenter (3 to 5 for redundancy per DC)

• WAN gossip is used to communicate over public internet or wide area network

• RPC - Remote Procedure Call. Request / response mechanism allowing a client to make a request of a server.

CONSUL

Image from www.consul.io and property of HashiCorp

AGENT RESPONSIBILITIES• Maintains its

• set of service

• check registrations

• health information

• Updates

• health checks

• local state

CATALOG• Backs Consuls service discovery

• Catalog is the service catalog

• Aggregates information submitted by agents.

• Maintains topology view of cluster,:

• Services available,

• Nodes which run those services (Node = Client Agent),

• Health information,

• Services and checks in catalog have less information than agent view

• Catalog is maintained only by server nodes (server agents).

• Catalog is replicated via Consul Consensus (RAFT, Serf)

AGENTS VS. CATALOG• Local agent state (agent client node) is different than catalog state (agent server

node)

• Local Agent notifies Catalog of changes. Updates are synced right away.

• Agents check to make sure its view of the world matches the catalog, and if not the catalog is updated

• Example: Registers a new service check with agent,

• Agent notifies catalog that this service check exists

• When a check is removed from the agent, it is removed from catalog

AGENTS VERSUS CATALOG 2

• If Agents run health checks, and status changes, then update is sent to catalog

• Agent is the authority of that node, and the services that exist on that node

• Scope

• Agent = Server or Virtual Machine

• Catalog = single datacenter, local area network, EC2 availability zone

• Changes are also synchronized periodically every minute to ten minutes

CONSUL COMMAND LINE

-server for server

mode

STARTING UP A NEW SERVER

• Expect min amount of servers for bootstrap

$ consul agent -server -data-dir=“/opt/git/dc1" -bootstrap-expect 5

HTTP / JSON API ENDPOINTS• kv - key value

• agent - api for dealing with agent

• catalog - dealing with datacenter catalog

• health - show health checks

• sessions, events, acl, status, etc.

CONFIG FILES

• config files can be stored locally and used to bootstrap config of consul

SERVICE DEFINITION

Default check is dead man switch or tll

HEALTH CHECKS• Dead man switch,

• time to live, you have to dial in with status update every X

• HTTP ping every N time

• HTTP Code 200 - 299 = PASS

• HTTP Code 429 = WARN

• anything else = FAIL

• Run a script every N:

• process 0 = pass,

• process 1 = warn,

• anything else = FAIL

SCRIPT CHECK

HTTP CHECK

DEAD MAN SWITCH CHECK

RPC PROTOCOL

• All command line options available via TCP/MsgPack

• MsgPack = binary JSON more or less

REGISTERING EXTERNAL SERVICES

External registry plus HTTP health check = integration of service that has no idea that Consul exists = Legacy integration of services = service discovery for legacy

services

WHAT WE HAVE DONE WITH CONSUL

• wrote java microservices lib that uses consul for service discovery

• Blog: Using Consul from QBit, the Java, JSON, WebSocket and REST microservice library, for health monitoring, clustering and service discovery

• used consul to implement clustered, replicated event bus for qbit

• Create general purpose service discovery that uses it

• Used general purpose service discovery to build distributed/clustered stats service to implement things like client application id rate limiting at high-speeds

THANK YOUhttp://www.linkedin.com/in/

rickhigh/en