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Consul for Service Discovery

Published / by tuxninja / Leave a Comment

Why Service Discovery ?

Service Discovery effectively replacing having to manually assign or automate your own DNS entries for nodes on your network. Service Discovery aims to move even further away from treating VM’s like pets to cattle, by getting rid of the age old practice Hostname & FQDN having contextual value. Instead when using services discovery nodes are automatically registered by an agent and automatically are configured in DNS for both nodes and services running on the machine.

Consul

Consul by Hashicorp is becoming the de-facto standard for Service Discovery. Consul’s full features & simplistic deployment model make it an optimal choice for organizations looking to quickly deploy Service Discovery capabilities in their environment.

Components of Consul

  1. The Consul Agent
  2. An optional JSON config file for each service located under /etc/consul.d/<service>.json
    1. If you do not specific a JSON file, consul can still start and will provide discovery for the nodes (they will have DNS as well)

A Quick Example of Consul

How easy is it to deploy console ?

  1. Download / Decompress and install the Consul agent – https://www.consul.io/downloads.html
  2. Define services in a JSON file (if you want) – https://www.consul.io/intro/getting-started/services.html
  3. Start the agent on the nodes – https://www.consul.io/intro/getting-started/join.html
  4.  Make 1 node join 1 other node (does not matter which node) to join the cluster, which gets you access to all cluster metadata

Steps 1 and 2 Above

  1. After downloading the Consul binary to each machine and decompressing it, copy it to /usr/local/bin/ so it’s in your path.
  2. Create the directory
  3. Optionally, run the following to create a JSON file defining a fake service running

Step 3 Above

Run the agent on each node, changing IP accordingly.

Step 4 Above

Wow, simple…ok now for the examples….

Show cluster members

Look up DNS for a node

Lookup DNS for a service

Query the REST API for Nodes

Query the REST API for Services

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