Consul is a service mesh solution providing a full featured control plane with service discovery, configuration, and segmentation functionality. Each of these features can be used individually as needed, or they can be used together to build a full service mesh. Consul requires a data plane and supports both a proxy and native integration model. Consul ships with a simple built-in proxy so that everything works out of the box, but also supports 3rd party proxy integrations such as Envoy.
You may be interested in our service mesh comparison article.
Consul is a distributed, highly available system. This section will cover the basics, purposely omitting some unnecessary detail, so you can get a quick understanding of how Consul works. For more detail, please refer to the in-depth architecture overview.
Every node that provides services to Consul runs a Consul agent. Running an agent is not required for discovering other services or getting/setting key/value data. The agent is responsible for health checking the services on the node as well as the node itself.
The agents talk to one or more Consul servers. The Consul servers are where data is stored and replicated. The servers themselves elect a leader. While Consul can function with one server, 3 to 5 is recommended to avoid failure scenarios leading to data loss. A cluster of Consul servers is recommended for each datacenter.
Components of your infrastructure that need to discover other services or nodes can query any of the Consul servers or any of the Consul agents. The agents forward queries to the servers automatically.
Each datacenter runs a cluster of Consul servers. When a cross-datacenter service discovery or configuration request is made, the local Consul servers forward the request to the remote datacenter and return the result.
Consul makes use of a HashiCorp service called Checkpoint which is used to check for updates and critical security bulletins. Only anonymous information, which cannot be used to identify the user or host, is sent to Checkpoint. An anonymous ID is sent which helps de-duplicate warning messages. This anonymous ID can be disabled. In fact, using the Checkpoint service is optional and can be disabled.
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