Add healthcheck command and add Docker HEALTHCHECK

Dockerfile

@@ -58,6 +58,8 @@ VOLUME [ "/data" ]
 
 EXPOSE 64210
 
+HEALTHCHECK --interval=30s --timeout=30s --start-period=5s --retries=3 CMD [ "cayley", "health" ]
+
 # Adding everything to entrypoint allows us to init, load and serve only with
 # arguments passed to docker run. For example:
 # `docker run cayleygraph/cayley --init -i /data/my_data.nq`

cmd/cayley/cayley.go

@@ -142,6 +142,7 @@ func init() {
 		command.NewHTTPCmd(),
 		command.NewConvertCmd(),
 		command.NewDedupCommand(),
+		command.NewHealthCmd(),
 	)
 	rootCmd.PersistentFlags().StringP("config", "c", "", "path to an explicit configuration file")