Coyote Point Systems Equalizer Especificaciones descargar pdf (Pagina 39)

sticky connections. If Equalizer does not find a sticky record, Equalizer proceeds to check all of the other clusters

that have the same IP address. If Equalizer still does not find a sticky record, it connects the user based on the

current load balancing policy.

Why a Server May Not Be Selected

There are several reasons that a server may not be selected by Equalizer:

1. The various configured health checks within Equalizer have detected that this server is "down". If a server

is marked down by a health check, it is immediately removed from the pool of servers available for load

balancing.

2. For Layer 4 clusters, if health checks have not yet detected that a server is down, and Equalizer is unable to

establish a cluster connection with the server, it will keep retrying the same server until the 4th SYN packet

received from the client and then use load balancing to select a new server. The whole connection

establishment must complete within stale_timeout seconds or the connection is dropped. If Equalizer

chooses a different server than the persistence record, it overwrites the persistence record to use the new

server for next time.

Note - Most clients will not have time to retry 3 times (send a 4th SYN packet) within the default 10 second stale

timeout window. Therefore the connection will be dropped and we will start the process over again when the next SYN

is received. (The 1st SYN would be at time 0, the 2nd at time 3, the 3rd at time 9… so the 4th would not happen before

10 seconds).

3. For Layer 7 clusters, if health checks have not yet detected that the server is down but Equalizer is unable

to establish a cluster connection with the server, it will wait for connect_timeout seconds and then drop the

connection so that the client can retry. If it receives an active refusal from the server (RST packet),

Equalizer will choose a different server and overwrite the persistence record to use the new server for next

time.

4. Maximum connections - If the maximum connections option is used for a server instance, and this server

already has that many active connections, it will not be used. This means that it will not be included in the

list of servers to select for load balancing. If persistence is in use, the strict_max_connections flag specifies

whether to persist to a server which already has more active connections than max_connections or to load

balance to a new server.

5. If the persist_override flag is selected in a server instance, and that server is selected by load balancing, the

client will not persist to this server even if persistence is enabled at the cluster level.

Geographic Load Balancing

The optional Envoy add-on enables requests to be automatically distributed across Equalizer sites in different

physical locations. An Equalizer site is a cluster of servers under single Equalizer’s control. A GeoCluster is a

collection of sites that provide a common service, such as Web sites. The various sites in a geographic cluster

can be hundreds or even thousands of miles apart. For example, a geographic cluster might contain two sites, one

in the east coast of the U.S. and one on the west coast of the U.S.

Equalizer Administration Guide

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Coyote Point Systems Equalizer Especificaciones Pagina 39