Coyote Point Systems Equalizer Spezifikationen PDF herunterladen (Seite 262)

Clusters

1. Equalizer has an idle timer for the established client connection, a connect timer to establish a server

connection, and an idle timer for the established server connection. Only one timeout is in use at any given

time. This is a summary of how timeouts are used when a client connects to Equalizer:

2. When a client successfully connects to a Virtual Cluster IP, the client timeout applies from the time the

connection is established until the client request headers are completely transmitted. Equalizer parses the

client's request, and verifies that the request is a valid HTTP request and that the information needed for

load balancing is obtained. In general, this happens at the time that the client headers are completed --

which is indicated by the client sending two blank lines for HTTP 1.0 or 1.1; one blank line for HTTP 0.9.

Once the headers are completely transmitted to Equalizer, the client timeout is no longer used.

3. As soon as the Equalizer is done examining the header data, it makes a connection to a server, as

determined by the load balancing policy, persistence, or a match rule hit. The amount of time that the

Equalizer tries to establish a connection to the server is the connect timeout. Once the server connection is

established, the connect timeout is no longer used.

4. After Equalizer establishes a connection with a server, the server timeout is the amount of time Equalizer

waits for the next bit of data from the server. Any response from the server restarts the server timeout.

The important distinction between the client timeout and the server timeout is that the client timeout is a “hard”

timeout -- the client has the number of seconds specified to transmit all of its headers to Equalizer before Equalizer

times out. This is done mainly for security considerations to prevent malicious clients from creating a large number

of partial connections and leaking data slowly over the connection, possibly causing resource exhaustion or other

undesirable effects on Equalizer.

The server timeout by contrast is a “soft” timeout -- the server has the number of seconds specified to send the next

piece of information (e.g., the next packet in the sequence). Whenever the client or the server sends a piece of

data on the connection, the server timeout is reset. This allows the server to send large data streams in small

pieces without timing out, and then close the connection once all the data is sent.

For example, when a client sends a POST operation in a request, the client timeout is used up until the time that

the POST headers have all been received. The connect timeout is used until a connection with the server is

established. Then, once the connection is established, the server timeout is used for the POST data itself and the

subsequent response from the server.

Note that there is the chance that a client will connect, send its headers, and then send continuous data to

Equalizer that repeatedly resets the server timeout. This vulnerability is usually avoided by setting a hard client

timeout on the application server itself (see "Cluster Connection Timeouts" on page 266).

The figure below summarizes the connection timeout parameters Equalizer uses for Layer 7 client and server

connections.

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Coyote Point Systems Equalizer Spezifikationen Seite 262