Using backup servers

The ecflow_client can be configured to contact alternate backup servers in case the primary server is not available – this typically most useful in Operational environments.

The use of backup servers is, by default, enabled only for Task commands. This behaviour can be customized by setting the environment variable ECF_HOSTFILE_POLICY. This variable can take the following values:

task (default): backup servers are used only for Task commands.
all: backup servers are used for all commands, including Task and User commands.

The list of backup servers can be specified by defining the environment variable ECF_HOSTFILE, indicating the location of a file, by convention located at $HOME/.ecf_hostfile, with the following format:

# This is a comment
host1             # port 3141 is used by default, when not specified
host2:port2
host3:port3

To enable the ecflow_client to read the file and use the listed backup servers, the environment variable ECF_HOSTFILE must be set before running the ecflow_client command:

export ECF_HOSTFILE=$HOME/.ecf_hostfile

Important

The maximum retry period is defined by ECF_TIMEOUT, which by default is set to 24 hours. This means that the ecflow_client will continue to loop over the list and retry primary host followed by alternate hosts for up to ECF_TIMEOUT, before giving up and reporting a failure.

Warning

When executing a command, the ecflow_client will always first try to connect to the primary host, as defined by command line options or ECF_HOST:ECF_PORT. If the first attemp to contact the primary host fails, the client will automatically retry contacting the primary server after waiting for a retry period of 10 seconds. Only after this second attempt has failed, will the ecflow_client then immediatelly try to connect to the backup servers listed in the ECF_HOSTFILE.

This implies that the ecflow_client will not try to connect to the backup servers immediately, and thus contacting the backup server incurs in a minimum 10 seconds delay.