'Server First', 'Client First' and 'Generic Streaming' protocols are the most basic L7 protocol types that Traffic Manager can use to manage traffic. They are useful when managing custom protocols or simple TCP connections because they do not expect the traffic to conform to any specific format.
This document describes the difference between Server First, Client First and Generic Streaming protocols, and explains some of the details of managing them.
Server-first protocols
Server-first is the simplest. When Traffic Manager receives a connection from a client, it immediately runs any TrafficScript rules, then immediately connects to a back-end server. It then listens on both connections (client-side and server-side) and passes data from one side to the other as it comes.
Load-balancing a simple server-first protocol, such as TIME or MySQL
Server-first protocols may be one-shot protocols such as Time (where the server writes the response data, then immediately closes the connection), or complex protocols like MySQL (where the server opens the dialog with a password challenge).
Client-first Protocols
Client-first is an optimization of server-first. On the client-side, Traffic Manager is only alerted when a connection has been established and data has been received. Traffic Manager then proceeds in the style of server-first, i.e. runs TrafficScript rules, connects to back-end and relays data back and forth. In practice, you can use server-first any time you use client-first, but client-first is more efficient when a client is expected to write the first data.
Load-balancing a client-first protocol such as HTTP
When you use a client-first procotol, you can use TrafficScript rules to inspect the client's request data before making your load-balancing decision.
Server-first with 'server banner'
Server-first with a 'server banner' is a different optimization (to cater for servers which broadcast a banner on connect, such as SMTP). When a client connects, Traffic Manager immediately writes the configured 'server-first banner' to the client, then proceeds as a regular client-first connection. In addition, Traffic Manager slurps and discards the first line or data (terminated by a \n) that the server sends.
Load-balancing a simple server-first protocol with a greeting banner, such as SMTP or FTP
Once again, you can use TrafficScript rules to inspect the client's request data before making your load-balancing decision.
Generic Streaming
Generic Streaming is a very basic connection handing mode that does not allow for any synchronization. It's best suited for long-lived asynchronous protocols where either party may initiate a transaction, such as WebSockets or chat protocols.
Load-balancing an unsynchronized protocol such as chat or websockets
If the protocol has a well-defined handshake (such as WebSockets) you can attach rules to manage the handshake. You can create rules that manage the subsequent, asynchronous packets but you should take care not to call TrafficScript functions that would block (such as request.read()) as these will stall data flowing in the other direction in the connection.
Troubleshooting Protocol problems
Timeouts
All connections have associated timeouts on connect and data. If a connect does not complete within the 'connect' timeout, or the connection is idle for the 'idle timeout', the connection will be discarded.
If it's a server-side connection, it will count as a server failure; three successive failures mark the node as dead.
The timeouts and 'three-failures' count can all be tuned if necessary via the Connection Management settings in the Virtual Server and Pool, and the Global Settings page.
Deadlocks
A request or response rule can cause the connection to block. For example, if Traffic Manager runs a request rule that calls 'request.read()', the connection will block until the required data has been read from the client. During this period, Traffic Manager stops relaying data from the server.
This may stall a connection or even trigger a timeout; be very careful if you use read (or write) TrafficScript functions with a bi-directional protocol.
Examples
The generic protocols typically function 'out-of-the-box' - all of the other protocols implemented by Traffic Manager layer on top of these and add protocol-specific handlers and optimizations.
Inspecting and managing generic protocols is challenging. The following articles describe such advanced use of these protocols:
