You may have to make changes to your custom servers to ensure that they
run correctly on a single system image; this is known as being SSI-compliant. Changes may be needed because the custom server work directory ($CUR_DIR/ca/cs_name_dir) will exist on
NFS, and it will be mounted on to each machine in the single system image.
There will be only one copy of the directory at one location, and that is
on the database server; this copy is made available to all clients through
NFS. Any configuration or data files located in this directory will therefore
be shared, and could cause problems to such custom servers running on a single
system image.
Follow these rules to make a custom server SSI-compliant:
- If the custom server or signaling process uses, or dynamically creates,
any files that exist within the mounted NFS file system, those files must
be able to cope with another running instance of themselves also creating
or writing to the same file at the same time. You can achieve this by file
locking and unlocking, by adding a host name to the file name, or by relocating
the file so it resides locally. Failure to do this causes one instance of
the software to interfere with another.
- If a process needs to store data that is specific to a particular client
node on the single system image, it must store it either on the local disk
or tag the file with the host name.
- The properties of a custom server are shared on all systems in the single
system image, so custom servers cannot have system-specific configuration
information passed by arguments specified in the properties window.