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SwarmKit

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SwarmKit is a toolkit for orchestrating distributed systems at any scale. It includes primitives for node discovery, raft-based consensus, task scheduling and more.

Its main benefits are:

  • Distributed: SwarmKit implements the Raft Consensus Algorithm in order to coordinate and does not rely on a single point of failure to perform decisions.
  • Secure: Node communication and membership within a Swarm are secure out of the box. SwarmKit uses mutual TLS for node authentication, role authorization and transport encryption, automating both certificate issuance and rotation.
  • Simple: SwarmKit is operationally simple and minimizes infrastructure dependencies. It does not need an external database to operate.

Overview

Machines running SwarmKit can be grouped together in order to form a Swarm, coordinating tasks with each other. Once a machine joins, it becomes a Swarm Node. Nodes can either be Worker Nodes or Manager Nodes.

  • Worker Nodes are responsible for running Tasks using an Executor. SwarmKit comes with a default Docker Container Executor that can be easily swapped out.
  • Manager Nodes on the other hand accept specifications from the user and are responsible for reconciling the desired state with the actual cluster state.

An operator can dynamically update a Node's role by promoting a Worker to Manager or demoting a Manager to Worker.

Tasks are organized in Services. A service is a higher level abstraction that allows the user to declare the desired state of a group of tasks. Services define what type of task should be created as well as how to execute them (e.g. run this many instances at all times) and how to update them (e.g. rolling updates).

Build

Requirements:

From the project root directory, run:

make binaries

Test

Before running tests for the first time, setup the tooling:

$ make setup

Then run:

$ make all

Usage Examples

3 Nodes Cluster

These instructions assume that swarmd and swarmctl are in your PATH.

(Before starting, make sure /tmp/node-N don't exist)

Initialize the first node:

$ swarmd -d /tmp/node-1 --listen-control-api /tmp/manager1/swarm.sock --hostname node-1

In two additional terminals, join two nodes (note: replace 127.0.0.1:4242 with the address of the first node)

$ swarmd -d /tmp/node-2 --hostname node-2 --join-addr 127.0.0.1:4242
$ swarmd -d /tmp/node-3 --hostname node-3 --join-addr 127.0.0.1:4242

In a fourth terminal, use swarmctl to explore and control the cluster. Before running swarmctl, set the SWARM_SOCKET environment variable to the path to the manager socket that was specified to --listen-control-api when starting the manager.

To list nodes:

$ export SWARM_SOCKET=/tmp/manager1/swarm.sock
$ swarmctl node ls
ID                         Name      Status  Availability
87pn3pug404xs4x86b5nwlwbr  node-1    READY   ACTIVE
by2ihzjyg9m674j3cjdit3reo  node-2    READY   ACTIVE
87pn3pug404xs4x86b5nwlwbr  node-3    READY   ACTIVE

Create and manage a service

Start a 'redis' service:

$ swarmctl service create --name redis --image redis

List the running services:

$ swarmctl service ls
ID                         Name   Image  Instances
--                         ----   -----  ---------
enf3gkwlnmasgurdyebp555ja  redis  redis  1

Inspect the service:

$ swarmctl service inspect redis
ID                : enf3gkwlnmasgurdyebp555ja
Name              : redis
Instances         : 1
Template
 Container
  Image           : redis

Task ID                      Service    Instance    Image    Desired State    Last State              Node
-------                      -------    --------    -----    -------------    ----------              ----
8oobrcr5u9lofmcbg7goaluyw    redis      1           redis    RUNNING          RUNNING 1 minute ago    node-1

Now change the instance count:

$ swarmctl service update redis --instances 4
enf3gkwlnmasgurdyebp555ja
$
$ swarmctl service inspect redis
ID                : enf3gkwlnmasgurdyebp555ja
Name              : redis
Instances         : 4
Template
 Container
  Image           : redis

Task ID                      Service    Instance    Image    Desired State    Last State               Node
-------                      -------    --------    -----    -------------    ----------               ----
8oobrcr5u9lofmcbg7goaluyw    redis      1           redis    RUNNING          RUNNING 2 minutes ago    node-1
cdv2oca2zc5upft24494orn1v    redis      2           redis    RUNNING          RUNNING 6 seconds ago    node-2
0x7e6a1d74nrwgcbbk9c12cqo    redis      3           redis    RUNNING          RUNNING 6 seconds ago    node-2
1c8zxfj0eifhbdxrgforqz4dp    redis      4           redis    RUNNING          RUNNING 6 seconds ago    node-1