vjagadish1989 commented on a change in pull request #903: SEP-19: Allocator
changes for standby-aware container allocation, and active container failover
URL: https://github.com/apache/samza/pull/903#discussion_r256082808
##########
File path:
samza-core/src/main/java/org/apache/samza/clustermanager/HostAwareContainerAllocator.java
##########
@@ -119,4 +153,219 @@ private void updateExpiryMetrics(SamzaResourceRequest
request) {
state.expiredPreferredHostRequests.incrementAndGet();
}
}
-}
+
+ // Method to run a container on the given resource if it meets all standby
constraints. If not, we re-request resource
+ // for the container (similar to the case when we re-request for a
launch-fail or request expiry).
+ private boolean
checkStandbyTaskConstraintsAndRunStreamProcessor(SamzaResourceRequest request,
String preferredHost,
+ SamzaResource samzaResource, SamzaApplicationState state) {
+
+ // If standby tasks are not enabled run streamprocessor and return true
+ if (!new JobConfig(config).getStandbyTasksEnabled()) {
+ runStreamProcessor(request, preferredHost);
+ return true;
+ }
+
+ String containerID = request.getContainerID();
+
+ if (checkStandbyConstraints(request, samzaResource, state)) {
+ // This resource can be used to launch this container
+ log.info("Running container {} on preferred host {} meets standby
constraints, launching on {}", containerID,
+ preferredHost, samzaResource.getHost());
+ runStreamProcessor(request, preferredHost);
+ state.successfulStandbyAllocations.incrementAndGet();
+ return true;
+ } else {
+ // This resource cannot be used to launch this container, so we treat it
like a launch fail, and issue an ANY_HOST request
+ log.info("Running container {} on host {} does not meet standby
constraints, cancelling resource request, releasing resource, and making a new
ANY_HOST request",
+ containerID, samzaResource.getHost());
+ resourceRequestState.releaseUnstartableContainer(samzaResource,
preferredHost);
+ resourceRequestState.cancelResourceRequest(request);
+ requestResourceDueToLaunchFailOrExpiredRequest(containerID);
+ state.failedStandbyAllocations.incrementAndGet();
+ return false;
+ }
+ }
+
+ // Helper method to check if this SamzaResourceRequest for a container can
be met on this resource, given standby
+ // container constraints, and the current set of pending and running
containers
+ private boolean checkStandbyConstraints(SamzaResourceRequest request,
SamzaResource samzaResource,
+ SamzaApplicationState samzaApplicationState) {
+ String containerIDToStart = request.getContainerID();
+ String host = samzaResource.getHost();
+ List<String> containerIDsForStandbyConstraints =
this.standbyContainerConstraints.get(containerIDToStart);
+
+ // Check if any of these conflicting containers are running/launching on
host
+ for (String containerID : containerIDsForStandbyConstraints) {
+ SamzaResource resource =
samzaApplicationState.pendingContainers.get(containerID);
+
+ // return false if a conflicting container is pending for launch on the
host
+ if (resource != null && resource.getHost().equals(host)) {
+ log.info("Container {} cannot be started on host {} because container
{} is already scheduled on this host",
+ containerIDToStart, samzaResource.getHost(), containerID);
+ return false;
+ }
+
+ // return false if a conflicting container is running on the host
+ resource = samzaApplicationState.runningContainers.get(containerID);
+ if (resource != null && resource.getHost().equals(host)) {
+ log.info("Container {} cannot be started on host {} because container
{} is already running on this host",
+ containerIDToStart, samzaResource.getHost(), containerID);
+ return false;
+ }
+ }
+
+ return true;
+ }
+
+ /**
+ * Intercept resource requests, which are due to either a launch-failure or
resource-request expired or standby
+ * 1. a standby container, we proceed to make a anyhost request
+ * 2. an activeContainer, we try to fail-it-over to a standby
+ * @param containerID Identifier of the container that will be run when a
resource is allocated
+ */
+ @Override
+ public void requestResourceDueToLaunchFailOrExpiredRequest(String
containerID) {
+ if (StandbyTaskUtil.isStandbyContainer(containerID)) {
+ log.info("Handling rerequesting for container {} using an any host
request");
+ super.requestResource(containerID, ResourceRequestState.ANY_HOST); //
proceed with a the anyhost request
+ } else {
+ requestResource(containerID, ResourceRequestState.ANY_HOST); // invoke
local method & select a new standby if possible
+ }
+ }
+
+ // Intercept issuing of resource requests from the CPM
+ // 1. for ActiveContainers and instead choose a StandbyContainer to stop
+ // 2. for a StandbyContainer (after it has been chosen for failover), to put
the active on the standby's host
+ // and request another resource for the standby
+ // 3. for a standbyContainer (if not for a failover)
+ @Override
Review comment:
would be preferable to not override `requestResource`..Additionally,
`requestResource` should not perform any actions related to failover handling.
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