Introduction to SNAplus2

SNAplus2 Components

 

In a domain with multiple SNAplus2 servers, one server holds the

 

master copy of the SNAplus2 domain configuration file. This server is

 

known as the master server. You can define other servers on the LAN to

 

be backup servers. The domain configuration file is copied to backup

 

servers—either when they are started, or when the master copy is

 

changed—so that all backup servers hold a copy of the latest

 

information.

 

In general, you should define at least one backup server in addition to

 

the master server. Any remaining servers can be defined as additional

 

backup servers, or they can be left as peer servers. A peer server obtains

 

domain configuration information from the master server as required,

 

but cannot act as a backup server.

 

If the master server fails, the first backup server on the list of servers

 

defined for the domain takes over as the master. The domain

 

configuration file on this server is used as the master copy, and is copied

 

to other servers as necessary. When the master server is restarted, it

 

receives a copy of the domain configuration from the backup server

 

currently acting as master, and then takes over as the master.

 

If at any time the master server and all backup servers are inactive, a

 

node on a peer server can still operate, and you can still change the

 

node's configuration. However, you cannot access the domain

 

configuration file, and therefore cannot access the configuration of

 

domain resources (as opposed to node resources). This means that you

 

cannot start the 3270 emulation program, start the RJE programs, or

 

allocate CPI-C conversations using symbolic destination names defined

 

in the configuration file.

 

If the LAN is split by a network failure into two noncommunicating

NOTE

 

domains, each containing one or more backup servers, SNAplus2 cannot

 

maintain a consistent configuration of domain resources across the LAN.

 

In this situation, each domain has an acting master server, each tracking

 

changes made to the domain configuration file in its own domain but

 

unaware of any changes made in the other domain. When the LAN

 

connection is re-established, the domain configuration file from the

 

original master server becomes the domain configuration file across the

 

LAN, and any domain resource files on other servers are overwritten. (If

 

the master is inactive at this point, the domain configuration file from

 

the highest backup server available in either of the two domains is used.)

 

Because changes to a domain configuration file are not necessarily

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