Deprecate the term "Ubernetes" in favor of "Cluster Federation" and "Multi-AZ Clusters"

This commit is contained in:
Quinton Hoole
2016-07-06 15:42:56 -07:00
parent 8c8c5d97ca
commit 791dd215d2
10 changed files with 80 additions and 74 deletions

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@@ -34,25 +34,25 @@ Documentation for other releases can be found at
# Kubernetes Multi-AZ Clusters
## (a.k.a. "Ubernetes-Lite")
## (previously nicknamed "Ubernetes-Lite")
## Introduction
Full Ubernetes will offer sophisticated federation between multiple kuberentes
Full Cluster Federation will offer sophisticated federation between multiple kuberentes
clusters, offering true high-availability, multiple provider support &
cloud-bursting, multiple region support etc. However, many users have
expressed a desire for a "reasonably" high-available cluster, that runs in
multiple zones on GCE or availability zones in AWS, and can tolerate the failure
of a single zone without the complexity of running multiple clusters.
Ubernetes-Lite aims to deliver exactly that functionality: to run a single
Multi-AZ Clusters aim to deliver exactly that functionality: to run a single
Kubernetes cluster in multiple zones. It will attempt to make reasonable
scheduling decisions, in particular so that a replication controller's pods are
spread across zones, and it will try to be aware of constraints - for example
that a volume cannot be mounted on a node in a different zone.
Ubernetes-Lite is deliberately limited in scope; for many advanced functions
the answer will be "use Ubernetes (full)". For example, multiple-region
Multi-AZ Clusters are deliberately limited in scope; for many advanced functions
the answer will be "use full Cluster Federation". For example, multiple-region
support is not in scope. Routing affinity (e.g. so that a webserver will
prefer to talk to a backend service in the same zone) is similarly not in
scope.
@@ -122,7 +122,7 @@ zones (in the same region). For both clouds, the behaviour of the native cloud
load-balancer is reasonable in the face of failures (indeed, this is why clouds
provide load-balancing as a primitve).
For Ubernetes-Lite we will therefore simply rely on the native cloud provider
For multi-AZ clusters we will therefore simply rely on the native cloud provider
load balancer behaviour, and we do not anticipate substantial code changes.
One notable shortcoming here is that load-balanced traffic still goes through
@@ -130,8 +130,8 @@ kube-proxy controlled routing, and kube-proxy does not (currently) favor
targeting a pod running on the same instance or even the same zone. This will
likely produce a lot of unnecessary cross-zone traffic (which is likely slower
and more expensive). This might be sufficiently low-hanging fruit that we
choose to address it in kube-proxy / Ubernetes-Lite, but this can be addressed
after the initial Ubernetes-Lite implementation.
choose to address it in kube-proxy / multi-AZ clusters, but this can be addressed
after the initial implementation.
## Implementation
@@ -182,8 +182,8 @@ region-wide, meaning that a single call will find instances and volumes in all
zones. In addition, instance ids and volume ids are unique per-region (and
hence also per-zone). I believe they are actually globally unique, but I do
not know if this is guaranteed; in any case we only need global uniqueness if
we are to span regions, which will not be supported by Ubernetes-Lite (to do
that correctly requires an Ubernetes-Full type approach).
we are to span regions, which will not be supported by multi-AZ clusters (to do
that correctly requires a full Cluster Federation type approach).
## GCE Specific Considerations
@@ -197,20 +197,20 @@ combine results from calls in all relevant zones.
A further complexity is that GCE volume names are scoped per-zone, not
per-region. Thus it is permitted to have two volumes both named `myvolume` in
two different GCE zones. (Instance names are currently unique per-region, and
thus are not a problem for Ubernetes-Lite).
thus are not a problem for multi-AZ clusters).
The volume scoping leads to a (small) behavioural change for Ubernetes-Lite on
The volume scoping leads to a (small) behavioural change for multi-AZ clusters on
GCE. If you had two volumes both named `myvolume` in two different GCE zones,
this would not be ambiguous when Kubernetes is operating only in a single zone.
But, if Ubernetes-Lite is operating in multiple zones, `myvolume` is no longer
But, when operating a cluster across multiple zones, `myvolume` is no longer
sufficient to specify a volume uniquely. Worse, the fact that a volume happens
to be unambigious at a particular time is no guarantee that it will continue to
be unambigious in future, because a volume with the same name could
subsequently be created in a second zone. While perhaps unlikely in practice,
we cannot automatically enable Ubernetes-Lite for GCE users if this then causes
we cannot automatically enable multi-AZ clusters for GCE users if this then causes
volume mounts to stop working.
This suggests that (at least on GCE), Ubernetes-Lite must be optional (i.e.
This suggests that (at least on GCE), multi-AZ clusters must be optional (i.e.
there must be a feature-flag). It may be that we can make this feature
semi-automatic in future, by detecting whether nodes are running in multiple
zones, but it seems likely that kube-up could instead simply set this flag.
@@ -218,14 +218,14 @@ zones, but it seems likely that kube-up could instead simply set this flag.
For the initial implementation, creating volumes with identical names will
yield undefined results. Later, we may add some way to specify the zone for a
volume (and possibly require that volumes have their zone specified when
running with Ubernetes-Lite). We could add a new `zone` field to the
running in multi-AZ cluster mode). We could add a new `zone` field to the
PersistentVolume type for GCE PD volumes, or we could use a DNS-style dotted
name for the volume name (<name>.<zone>)
Initially therefore, the GCE changes will be to:
1. change kube-up to support creation of a cluster in multiple zones
1. pass a flag enabling Ubernetes-Lite with kube-up
1. pass a flag enabling multi-AZ clusters with kube-up
1. change the kuberentes cloud provider to iterate through relevant zones when resolving items
1. tag GCE PD volumes with the appropriate zone information

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@@ -34,7 +34,7 @@ Documentation for other releases can be found at
# Kubernetes Cluster Federation
## (a.k.a. "Ubernetes")
## (previously nicknamed "Ubernetes")
## Requirements Analysis and Product Proposal
@@ -413,7 +413,7 @@ detail to be added here, but feel free to shoot down the basic DNS
idea in the mean time. In addition, some applications rely on private
networking between clusters for security (e.g. AWS VPC or more
generally VPN). It should not be necessary to forsake this in
order to use Ubernetes, for example by being forced to use public
order to use Cluster Federation, for example by being forced to use public
connectivity between clusters.
## Cross-cluster Scheduling
@@ -546,7 +546,7 @@ prefers the Decoupled Hierarchical model for the reasons stated below).
here, as each underlying Kubernetes cluster can be scaled
completely independently w.r.t. scheduling, node state management,
monitoring, network connectivity etc. It is even potentially
feasible to stack "Ubernetes" federated clusters (i.e. create
feasible to stack federations of clusters (i.e. create
federations of federations) should scalability of the independent
Federation Control Plane become an issue (although the author does
not envision this being a problem worth solving in the short
@@ -595,7 +595,7 @@ prefers the Decoupled Hierarchical model for the reasons stated below).
![image](federation-high-level-arch.png)
## Ubernetes API
## Cluster Federation API
It is proposed that this look a lot like the existing Kubernetes API
but be explicitly multi-cluster.
@@ -603,7 +603,8 @@ but be explicitly multi-cluster.
+ Clusters become first class objects, which can be registered,
listed, described, deregistered etc via the API.
+ Compute resources can be explicitly requested in specific clusters,
or automatically scheduled to the "best" cluster by Ubernetes (by a
or automatically scheduled to the "best" cluster by the Cluster
Federation control system (by a
pluggable Policy Engine).
+ There is a federated equivalent of a replication controller type (or
perhaps a [deployment](deployment.md)),
@@ -627,14 +628,15 @@ Controllers and related Services accordingly).
This should ideally be delegated to some external auth system, shared
by the underlying clusters, to avoid duplication and inconsistency.
Either that, or we end up with multilevel auth. Local readonly
eventually consistent auth slaves in each cluster and in Ubernetes
eventually consistent auth slaves in each cluster and in the Cluster
Federation control system
could potentially cache auth, to mitigate an SPOF auth system.
## Data consistency, failure and availability characteristics
The services comprising the Ubernetes Control Plane) have to run
The services comprising the Cluster Federation control plane) have to run
somewhere. Several options exist here:
* For high availability Ubernetes deployments, these
* For high availability Cluster Federation deployments, these
services may run in either:
* a dedicated Kubernetes cluster, not co-located in the same
availability zone with any of the federated clusters (for fault
@@ -672,7 +674,7 @@ does the zookeeper config look like for N=3 across 3 AZs -- and how
does each replica find the other replicas and how do clients find
their primary zookeeper replica? And now how do I do a shared, highly
available redis database? Use a few common specific use cases like
this to flesh out the detailed API and semantics of Ubernetes.
this to flesh out the detailed API and semantics of Cluster Federation.
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@@ -79,10 +79,11 @@ The design of the pipeline for collecting application level metrics should
be revisited and it's not clear whether application level metrics should be
available in API server so the use case initially won't be supported.
#### Ubernetes
#### Cluster Federation
Ubernetes might want to consider cluster-level usage (in addition to cluster-level request)
of running pods when choosing where to schedule new pods. Although Ubernetes is still in design,
The Cluster Federation control system might want to consider cluster-level usage (in addition to cluster-level request)
of running pods when choosing where to schedule new pods. Although
Cluster Federation is still in design,
we expect the metrics API described here to be sufficient. Cluster-level usage can be
obtained by summing over usage of all nodes in the cluster.