Multihost tasks

Feature Requirements

The multihost feature is brought to you by Beaker and the test harness (e.g. Restraint). Multihosting is mostly performed on the test harness itself. This section provides an overview of how multihost works with the currently supported test harness. If your test harness does not support task synchronization, then this section can be ignored. If you are using only the test harness and not beaker, this section describes a work-around.


Beaker has support for tasks that run on multiple hosts to test the interactions of a client and a server. When a multihost task is run in the lab, one or more machines will be allocated to each role in the test. Each machine has its own recipe and these recipes are defined within a recipeset in a single job.

Each machine under test may want to synchronize to ensure that they start the test together, and may need to synchronize at various stages within the test. While Beaker doesn’t assign any particular semantics to role names (it just uses them to set the corresponding task environment variables), there are three common roles used in many multi-host tests: client, server and driver.

For many purposes, all you will need are client and server roles. For a test involving one or more clients talking to one or more servers, a typical approach would be for the clients to block while the servers get ready. Once all servers are ready, the clients perform the testing they need using the services provided by the server machines. The servers block waiting for clients to finish while in parallel carrying out work requested by the clients. In conclusion, the clients eventually report results back to the test. Once all clients have finished testing, the server tests unblock and report their results.

Each participant in a test will report results within the same job and report to different places within the result hierarchy. For example, the server part of the test may PASS if it survives the load, but the client part might FAIL upon, say, getting erroneous data from the server; this would lead to an overall FAIL for the test.

If you have a more complex arrangement, it is possible to have a driver machine which controls all of the testing.

All of the participants in a multihost test share a single, which performs every role within the test (e.g. the client role and server role). When a multihost test is run in the lab, the framework automatically sets environment variables to allow the various participants to know what their role should be, which other machines they should be talking to, and what roles those other machines are performing in the test. You will need to have logic in your to examine the role variables and perform the necessary role accordingly.

You can choose to perform your own synchronization or have the harness (e.g. restraint) perform task synchronization for you. If you want the harness to perform synchronization, the role=SERVERS and role=CLIENTS are required in your job recipes/tasks. The harness performs synchronization of servers and clients at the completion of the task. The tasks will all block at the end until the last one has finished. They will then move onto the next task but not in unison since some may be sleeping before rechecking the status of others.

Environment Variables for Synchronization

The following environment variables are shared by all instances of the within a recipeset for harness controlled synchronization. If you choose different role names than CLIENTS/SERVERS, your tasks are responsible for synchronization actions as described later. However, the harness with beaker’s help, will still export role enviroment variables with your chosen names and wlll separate FQDNs with a space.


Contains a space-separated list of FQDNs of clients within this recipeset (that is, systems running recipes marked with the CLIENTS role in the job XML).


Contains a space-separated list of FQDNs of servers within this recipeset (that is, systems running recipes marked with the SERVERS role in the job XML).


Contains the FQDN for the driver of this recipe set, if any (that is, a system running a recipe marked with the DRIVER role in the job XML).

When writing your own synchronization, you can use the variable HOSTNAME in your to determine its identity. HOSTNAME is set by the harness task environment plugin, and is unique for each host within a recipeset. Your test can use HOSTNAME to search the client, server, or driver environment variables to determine its role. An example of this is shown later in Handling Environment Variables in your synchronized

When you are developing your test outside the lab environment, only HOSTNAME is set for you (when sourcing the script). One way to run multihost tests outside a Beaker instance is to copy the test to multiple development machines, set up CLIENTS, SERVERS, and DRIVER manually within a shell on each machine, and then manually run the on each one, debugging as necessary. Alternatively, support for standalone testing may be added directly to the test script, as described in Standalone execution of multihost tests.

Simple job.xml for Synchronization

In its simplest form, a job with multihost testing may look something like:

     <recipe role='MYSERVERS'>
        <task name='/distribution/check-install'/>
        <task name='/my/multihost/test'/>
     <recipe role='MYCLIENTS'>
        <task name='/distribution/check-install'/>
        <task name='/my/multihost/test'/>


For brevity some necessary parts are left out in the above job definition. See Job XML for details.

As there is only one recipe in the recipe set with each defined role, submitting the job above will export environmental variables MYSERVERS and MYCLIENTS set to their respective FQDNs.

If you replace the roles with SERVERS/CLIENTS, the harness will perform synchronization operations for you. In this case, roles MYSERVERS/MYCLIENTS are used instead to begin showing you how to perform synchronization on your own without harness end-of-task synchronization.

Any multihost testing must ensure that the task execution order aligns correctly on all machines. This includes synchronization controlled by the harness. For example, the below will fail:

  <task role='STANDALONE' name='/distribution/check-install'/>
  <task role='STANDALONE' name='/my/test/number1'/>
  <task role='MYSERVERS'  name='/my/multihost/test'/>
  <task role='STANDALONE' name='/distribution/check-install'/>
  <task role='MYCLIENTS'  name='/my/multihost/test'/>

This will fail because the multihost test is the third test on the server side and it’s the second test on the client side. To fix this, you can pad in dummy test cases on the side that has fewer test cases. There is a dummy test that lives in /distribution/utils/dummy for this purpose. So, the above can be fixed as:

 <task role='STANDALONE' name='/distribution/check-install'/>
 <task role='STANDALONE' name='/my/test/number1'/>
 <task role='MYSERVERS'  name='/my/multihost/test'/>
 <task role='STANDALONE' name='/distribution/check-install'/>
 <task role='STANDALONE' name='/distribution/utils/dummy'/>
 <task role='MYCLIENTS'  name='/my/multihost/test'/>

Handling Environment Variables in your synchronized

In the sample job.xml provided previously, the in /my/multihost/test test might look like:

Server() {
    # .. server code here

Client() {
    # .. client code here

if test -z "$JOBID" ; then
    echo "Variable jobid not set! Assume developer mode"

if [ -z "$MYSERVERS" -o -z "$MYCLIENTS" ]; then
    echo "Can not determine test type! Client/Server Failed:"
    report_result $TEST $RESULT

if $(echo $MYSERVERS | grep -q $:envvar:`HOSTNAME`); then

if $(echo $MYCLIENTS | grep -q $:envvar:`HOSTNAME`); then

We have Server() and Client() functions which will be executed by recipes with the MYSERVERS and MYCLIENTS role respectively.

Then we test for JOBID which indicates if the script is running inside a Beaker instance; otherwise, it’s being run on the test developer’s local workstation or any other non-Beaker system.

The tests comparing MYSERVERS and MYCLIENTS to HOSTNAME determine what code to run on this particular machine. As mentioned before, since only one recipe in our recipe set uses each role, the MYSERVERS and MYCLIENTS environmental variables will be set to their respective machines’ names and exported on both machines.

Writing User-Defined Synchronization in your

For most meaningful multi-host tests, there has to be some sort of coordination and synchronization between the machines and the execution of the test code on both sides. While in some cases, this may be handled by a dedicated recipe with the MYDRIVER role, the restraint harness offers two utilities for this purpose: rstrnt-sync-set and rstrnt-sync-block.

The rstrnt-sync-set command is used to set a state on a machine. The rstrnt-sync-block command is used to block the execution of the task until a certain state on certain machine(s) is reached. Those familiar with parallel programming can think of this as a barrier operation. A brief overview of the usage of these utilities follows:

  • rstrnt-sync-set: This command sets the state of the current machine to an arbitrary text string.

    Syntax: rstrnt-sync-set -s STATE

  • rstrnt-sync-block: This command blocks execution and doesn’t return until the specified STATE is set on the specified machine(s).

    Syntax: rstrnt-sync-block -s STATE [-s STATE1 -s STATE2] machine1 machine2 ...

For details on the options provided by the restraint harness, refer to Restraint Command documentation and search for these commands.

The role related environment variables are useful here as they contain the hostnames of all recipes in the recipeset with that role. For example, you can wait for all recipes with the MYSERVERS role to set their state to "READY" by running:

rstrnt-sync-block -s READY $MYSERVERS

By default the rstrnt-sync-block utility will block until the local or external watchdog is triggered if the expected state is never achieved. If this behavior isn’t desired, the –timeout option can be used instead. In that case, a zero return code indicates that the desired state was reached, while a non-zero return code indicates the operation timed out.

These commands require a bit of manual intervention when run in the standalone execution environment for Beaker task development, as the Beaker lab controller normally coordinates the barrier operation. See Standalone execution of multihost tests.

Sample for a user synchronized multihost task

# Source the common test script helpers
. /usr/bin/

# Save STDOUT and STDERR, and redirect everything to a file.
exec 5>&1 6>&2
exec >> "${OUTPUTFILE}" 2>&1

    echo "-- wait the server to finish."
    rstrnt-sync-block -s "DONE" ${MYSERVERS}

    for i in ${MYSERVERS}
        echo "-- finger user \"$user\" from server \"${i}\"."
        ./finger_client "${i}" "${user}"
        # It returns non-zero for failure.
        if [ $? -ne 0 ]; then
            rstrnt-sync-set -s "DONE"
            report_result "${TEST}" "FAIL" 0
            exit 1

    echo "-- client finishes."
    rstrnt-sync-set -s "DONE"

    # Start server and check it is up and running.
    /sbin/chkconfig finger on && sleep 5
    if ! netstat -a | grep "finger" ; then
        rstrnt-sync-set -s "DONE"
        report_result "${TEST}" "FAIL" 0
        exit 1
    useradd finger1
    echo "-- server finishes."
    rstrnt-sync-set -s "DONE"
    rstrnt-sync-block -s "DONE" ${MYCLIENTS}

# ---------- Start Test -------------
if echo "${MYCLIENTS}" | grep "${:envvar:`HOSTNAME`}" >/dev/null; then
    echo "-- run finger test as client."
if echo "${MYSERVERS}" | grep "${:envvar:`HOSTNAME`}" >/dev/null; then
    echo "-- run finger test as server."
echo "--- end of"
report_result "${TEST}" "${result}" 0
exit 0

Standalone execution of multihost tests

Multihost tests can be more easily executed outside a Beaker instance by altering their behavior based on the JOBID variable (or any other documented variable which is set when running inside a Beaker instance).

For a two machine test that uses the CLIENTS and SERVERS roles, you could create a pair of local virtual machines and add the following lines at the beginning of your script:

# decide if we're running standalone or in a Beaker instance
if test -z $JOBID ; then
        echo "Variable JOBID not set, assuming standalone"
        echo "Variable JOBID set, we're running inside Beaker"
echo "Clients: $CLIENTS"
echo "Servers: $SERVERS"

# ... rest of test script