17793bccb9
Automatic merge from submit-queue (batch tested with PRs 41830, 42630)
Arrange for elasticsearch to shutdown cleanly
Kubernetes initiates "graceful shutdown" by sending SIGTERM to pid 1, which
is exactly what elasticsearch is expecting (good!)
The way the existing startup scripts worked however, this signal arrived at
the shell wrapper, not elasticsearch, and the shell wrapper exited,
killing the container immediately (bad!)
Before this change:
```
1 ? Ss 0:00 /bin/sh -c /run.sh
6 ? S 0:00 /bin/bash /run.sh
13 ? S 0:00 \_ /bin/su -c /elasticsearch/bin/elasticsearch elasticsearch
14 ? Ss 0:00 \_ sh -c /elasticsearch/bin/elasticsearch
15 ? Sl 19:18 \_ /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java ... org.elasticsearch.bootstrap.Elasticsearch start
```
After this change:
```
1 ? Ssl 0:29 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java ... org.elasticsearch.bootstrap.Elasticsearch start
```
Cluster add-ons
Overview
Cluster add-ons are resources like Services and Deployments (with pods) that are shipped with the Kubernetes binaries and are considered an inherent part of the Kubernetes clusters.
There are currently two classes of add-ons:
- Add-ons that will be reconciled.
- Add-ons that will be created if they don't exist.
More details could be found in addon-manager/README.md.
Cooperating Horizontal / Vertical Auto-Scaling with "reconcile class addons"
"Reconcile" class addons will be periodically reconciled to the original state given
by the initial config. In order to make Horizontal / Vertical Auto-scaling functional,
the related fields in config should be left unset. More specifically, leave replicas
in ReplicationController / Deployment / ReplicaSet unset for Horizontal Scaling,
leave resources for container unset for Vertical Scaling. The periodic reconcile
won't clobbered these fields, hence they could be managed by Horizontal / Vertical
Auto-scaler.
Add-on naming
The suggested naming for most of the resources is <basename> (with no version number).
Though resources like Pod, ReplicationController and DaemonSet are exceptional.
It would be hard to update Pod because many fields in Pod are immutable. For
ReplicationController and DaemonSet, in-place update may not trigger the underlying
pods to be re-created. You probably need to change their names during update to trigger
a complete deletion and creation.