apache/cassandra · error · IllegalStateException

Missing host

Error message

Missing host

What it means

Thrown by Server.getSocket() when a port was provided but no host address was set, so the builder cannot construct the bind InetSocketAddress. Like the missing-port case, it surfaces as an IllegalStateException at server start rather than at builder time, indicating incomplete server configuration.

Solutions

1. Call Server.Builder.host(InetAddress) (or equivalent) with the address to bind, e.g. the local RPC address
2. Or supply a full InetSocketAddress via the socket(...) builder method
3. Use InetAddress.getLoopbackAddress() in test harnesses if binding to all interfaces is not intended
4. Validate builder fields before start() in embedding code

Example fix

// before
Server.builder().withPort(9042).build();
// after
Server.builder().withPort(9042).withHost(InetAddress.getLocalHost()).build();

if (builderHost == null) throw new IllegalArgumentException("Server.Builder requires a host; call host(...) or socket(...)");

boolean readyToBuild(Server.Builder b) { return b.getHostAddr() != null && b.getPort() != -1; }

try { server.start(); } catch (IllegalStateException e) { if (e.getMessage().equals("Missing host")) { fixBuilderConfig(); } else throw e; }

When it happens

Trigger: Server.Builder built with port(...) but no hostAddr and no explicit socket; getSocket() reaches the else branch because this.hostAddr is null while this.port != -1.

Common situations: Embedding the transport in tests/tools with only a port configured, refactoring away a host constant, or assuming the server will default to binding all interfaces (it will not here).

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Missing port number
• be positive
• native_transport_min_backoff_on_queue_overload should be…
• a hints file cannot be configured for both compression and…
• A maximum number of tokens per node is supported

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/89c08d744d5ae0ed. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/transport/Server.java:292

        }

        public Server build()
        {
            return new Server(this);
        }

        private InetSocketAddress getSocket()
        {
            if (this.socket != null)
                return this.socket;
            else
            {
                if (this.port == -1)
                    throw new IllegalStateException("Missing port number");
                if (this.hostAddr != null)
                    this.socket = new InetSocketAddress(this.hostAddr, this.port);
                else
                    throw new IllegalStateException("Missing host");
                return this.socket;
            }
        }
    }

    public static class ConnectionTracker implements Connection.Tracker
    {
        private static final ChannelMatcher PRE_V5_CHANNEL = channel -> channel.attr(Connection.attributeKey)
                                                                               .get()
                                                                               .getVersion()
                                                                               .isSmallerThan(ProtocolVersion.V5);

        // TODO: should we be using the GlobalEventExecutor or defining our own?
        public final ChannelGroup allChannels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
        private final EnumMap<Event.Type, ChannelGroup> groups = new EnumMap<>(Event.Type.class);
        private final ProtocolVersionTracker protocolVersionTracker = new ProtocolVersionTracker();
        private final BooleanSupplier isRunning;

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