public static InferredTokenOwnership inferTokenOwnerFromGossip()

in priam/src/main/java/com/netflix/priam/identity/token/TokenRetrieverUtils.java [35:112]
54 lines of code
8 McCabe index (conditional complexity)

    public static InferredTokenOwnership inferTokenOwnerFromGossip(
            ImmutableSet<PriamInstance> allIds, String token, String dc) {

        // Avoid using dead instance who we are trying to replace (duh!!)
        // Avoid other regions instances to avoid communication over public ip address.
        List<? extends PriamInstance> eligibleInstances =
                allIds.stream()
                        .filter(priamInstance -> !token.equalsIgnoreCase(priamInstance.getToken()))
                        .filter(priamInstance -> priamInstance.getDC().equalsIgnoreCase(dc))
                        .collect(Collectors.toList());
        // We want to get IP from min 1, max 3 instances to ensure we are not relying on
        // gossip of a single instance.
        // Good idea to shuffle so we are not talking to same instances every time.
        Collections.shuffle(eligibleInstances);
        // Potential issue could be when you have about 50% of your cluster C* DOWN or
        // trying to be replaced.
        // Think of a major disaster hitting your cluster. In that scenario chances of
        // instance hitting DOWN C* are much much higher.
        // In such a case you should rely on @link{CassandraConfig#setReplacedIp}.
        int noOfInstancesGossipShouldMatch = Math.max(1, Math.min(3, eligibleInstances.size()));

        // While it is ideal to check all the nodes in the ring to see if they agree on
        // the IP to be replaced, in large clusters it may affect the startup
        // performance. So we pick three random hosts from the ring and see if they all
        // agree on the IP to be replaced. If not, we don't replace.
        InferredTokenOwnership inferredTokenOwnership = new InferredTokenOwnership();
        int matchedGossipInstances = 0, reachableInstances = 0;
        for (PriamInstance instance : eligibleInstances) {
            logger.info("Finding down nodes from ip[{}]; token[{}]", instance.getHostIP(), token);

            try {
                TokenInformation tokenInformation =
                        getTokenInformation(instance.getHostIP(), token);
                reachableInstances++;

                if (inferredTokenOwnership.getTokenInformation() == null) {
                    inferredTokenOwnership.setTokenInformation(tokenInformation);
                }

                if (inferredTokenOwnership.getTokenInformation().equals(tokenInformation)) {
                    matchedGossipInstances++;
                    if (matchedGossipInstances == noOfInstancesGossipShouldMatch) {
                        inferredTokenOwnership.setTokenInformationStatus(
                                InferredTokenOwnership.TokenInformationStatus.GOOD);
                        return inferredTokenOwnership;
                    }
                } else {
                    // Mismatch in the gossip information from Cassandra.
                    inferredTokenOwnership.setTokenInformationStatus(
                            InferredTokenOwnership.TokenInformationStatus.MISMATCH);
                    logger.info(
                            "There is a mismatch in the status information reported by Cassandra. TokenInformation1: {}, TokenInformation2: {}",
                            inferredTokenOwnership.getTokenInformation(),
                            tokenInformation);
                    inferredTokenOwnership.setTokenInformation(
                            inferredTokenOwnership.getTokenInformation().isLive
                                    ? inferredTokenOwnership.getTokenInformation()
                                    : tokenInformation);
                    return inferredTokenOwnership;
                }

            } catch (GossipParseException e) {
                logger.warn(e.getMessage());
            }
        }

        // If we are not able to reach at least minimum required instances.
        if (reachableInstances < noOfInstancesGossipShouldMatch) {
            inferredTokenOwnership.setTokenInformationStatus(
                    InferredTokenOwnership.TokenInformationStatus.UNREACHABLE_NODES);
            logger.info(
                    String.format(
                            "Unable to find enough instances where gossip match. Required: [%d]",
                            noOfInstancesGossipShouldMatch));
        }

        return inferredTokenOwnership;
    }