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Discovery Service

The Discovery service is automatically included in every Cycle environment.

Service discovery is an essential part of containerized deployments. The discovery service is responsible for dynamic hostname to IP translation and DNS lookups. This allows Cycle to provide geograpically-agnostic private networks for each environment.

When a container is created & started, Cycle creates a file inside the container, /etc/resolv.conf, that tells the container to use the Discovery service for all DNS lookups. Therefore, a lookup to another container with the hostname frontend can be made by simply using frontend as the domain name. Because of the entry made to the /etc/resolv.conf file, the initial dns query made by the requesting container will use the discovery service to resolve the lookup. The discovery service will return all known IP's for the lookup, sorted by proximity to the requesting instance.

If there is no entry that matches, the nameservers will fall back to Google's DNS (8.8.8.8) for all other queries.

The discovery service caches queries for 5 minutes, giving a performance boost for repeated lookups, since they will be served over the private network.

sequenceDiagram participant Cycle participant User Container One participant User Container Two participant Discovery Cycle->>User Container One: Installing /etc/resolve.conf Cycle->>User Container Two: Installing /etc/resolve.conf User Container One->>Discovery: Whats the IP of User Container Two Discovery->>User Container One: Here is a list of all IP's I have for that container Note left of User Container One: IP List: [10.0.11.100, 10.0.11.101] User Container One->>User Container Two: Request files from http://10.0.11.100/static/file

Forcing Random IP Order From Discovery​

When discovery returns a list of IP's after a DNS lookup the list is sorted by proximity to the requesting instance. If the user would like that list to be randomized prepend the hostname with an underscore - ex: _hostname.