Initial UnknownHostException is Unrecoverable

RawSocketSender のコンストラクターとその connect() メソッドから始め、特にサーバーアドレスがどのように保存され、再利用されるかを確認してください。初回のホスト名解決に失敗した場合と、フェイルオーバー中に DNS が変更された場合の動作を検証してください。再接続で古い解決済みアドレスではなく、現在のホスト名解決が使用されれば完了です。

The RawSocketSender takes a host and port in its constructor and coverts these into an InetSocketAddress, which tries to resolve the hostname. On RawSocketSender connect this InetSocketAddress is used to reconnect, but if it wasn't resolved during fluent-logger init then it will fail over and over. The code snipped from RawSocketSender is below:

public RawSocketSender(String host, int port, int timeout, int bufferCapacity, Reconnector reconnector) {
    msgpack = new MessagePack();
    msgpack.register(Event.class, Event.EventTemplate.INSTANCE);
    pendings = ByteBuffer.allocate(bufferCapacity);
    server = new InetSocketAddress(host, port); // Create InetSocketAddress on init
    this.reconnector = reconnector;
    name = String.format("%s_%d_%d_%d", host, port, timeout, bufferCapacity);
    this.timeout = timeout;
}

private void connect() throws IOException {
    try {
        socket = new Socket();
        socket.connect(server, timeout); // Reconnection uses pre-resolved server field
        out = new BufferedOutputStream(socket.getOutputStream());
    } catch (IOException e) {
        throw e;
    }
}

This issue comes up when using the fluent-logger in a highly dynamic environment (like on Docker Swarm) where apps may come up before a DNS entry in Consul is even resolvable. It also means that during failover of a Fluent host (triggering a DNS change) the then failing socket connection will always try the old Fluent host IP and never re-resolve the DNS entry.

My recommendation is to store the Fluent host and port as private fields within the RawSocketSender, not a resolved InetSocketAddress (now stored as this.server) and create a new InetSocketAddress on every socket connection.

I understand there will be performance implications of this and am happy to submit a PR, but wanted to bring it up in an issue in case there were reasons for implementing the RawSocketSender the current way.