Kubemark is a performance testing tool which allows users to run experiments on simulated clusters. The primary use case is scalability testing, as simulated clusters can be much bigger than the real ones. The objective is to expose problems with the master components (API server, controller manager or scheduler) that appear only on bigger clusters (e.g. small memory leaks).
This document serves as a primer to understand what Kubemark is, what it is not, and how to use it.
On a very high level Kubemark cluster consists of two parts: real master components and a set of “Hollow” Nodes. The prefix “Hollow” means an implementation/instantiation of a component with all “moving” parts mocked out. The best example is HollowKubelet, which pretends to be an ordinary Kubelet, but does not start anything, nor mount any volumes - it just lies it does. More detailed design and implementation details are at the end of this document.
Currently master components run on a dedicated machine(s), and HollowNodes run on an ‘external’ Kubernetes cluster. This design has a slight advantage, over running master components on external cluster, of completely isolating master resources from everything else.
To run Kubemark you need a Kubernetes cluster (called external cluster)
for running all your HollowNodes and a dedicated machine for a master.
Master machine has to be directly routable from HollowNodes. You also need an
access to some Docker repository.
Currently scripts are written to be easily usable by GCE, but it should be relatively straightforward to port them to different providers or bare metal.
Common workflow for Kubemark is:
- starting a Kubemark cluster (on GCE)
- running e2e tests on Kubemark cluster
- monitoring test execution and debugging problems
- turning down Kubemark cluster
Included in descriptions there will be comments helpful for anyone who’ll want to port Kubemark to different providers.
To start a Kubemark cluster on GCE you need to create an external kubernetes
cluster (it can be GCE, GKE or anything else) by yourself, make sure that kubeconfig
points to it by default, build a kubernetes release (e.g. by running
make quick-release) and run test/kubemark/start-kubemark.sh script.
This script will create a VM for master components, Pods for HollowNodes
and do all the setup necessary to let them talk to each other. It will use the
configuration stored in cluster/kubemark/config-default.sh - you can tweak it
however you want, but note that some features may not be implemented yet, as
implementation of Hollow components/mocks will probably be lagging behind ‘real’
one. For performance tests interesting variables are NUM_NODES and
MASTER_SIZE. After start-kubemark script is finished you’ll have a ready
Kubemark cluster, a kubeconfig file for talking to the Kubemark cluster is
stored in test/kubemark/kubeconfig.kubemark.
Currently we're running HollowNode with limit of 0.05 a CPU core and ~60MB or memory, which taking into account default cluster addons and fluentD running on an 'external' cluster, allows running ~17.5 HollowNodes per core.
Start-kubemark script does quite a lot of things:
-
Creates a master machine called hollow-cluster-master and PD for it (uses gcloud, should be easy to do outside of GCE)
-
Creates a firewall rule which opens port 443* on the master machine (uses gcloud, should be easy to do outside of GCE)
-
Builds a Docker image for HollowNode from the current repository and pushes it to the Docker repository (GCR for us, using scripts from
cluster/gce/util.sh- it may get tricky outside of GCE) -
Generates certificates and kubeconfig files, writes a kubeconfig locally to
test/kubemark/kubeconfig.kubemarkand creates a Secret which stores kubeconfig for HollowKubelet/HollowProxy use (used gcloud to transfer files to Master, should be easy to do outside of GCE). -
Creates a ReplicationController for HollowNodes and starts them up. (will work exactly the same everywhere as long as MASTER_IP will be populated correctly, but you’ll need to update docker image address if you’re not using GCR and default image name)
-
Waits until all HollowNodes are in the Running phase (will work exactly the same everywhere)
* Port 443 is a secured port on the master machine which is used for all external communication with the API server. In the last sentence external means all traffic coming from other machines, including all the Nodes, not only from outside of the cluster. Currently local components, i.e. ControllerManager and Scheduler talk with API server using insecure port 8080.
To run standard e2e test on your Kubemark cluster created in the previous step
you execute test/kubemark/run-e2e-tests.sh script. It will configure ginkgo to
use Kubemark cluster instead of something else and start an e2e test. This
script should not need any changes to work on other cloud providers.
By default (if nothing will be passed to it) the script will run a Density '30
test. If you want to run a different e2e test you just need to provide flags you want to be
passed to hack/ginkgo-e2e.sh script, e.g. --ginkgo.focus="Load" to run the
Load test.
By default, at the end of each test, it will delete namespaces and everything
under it (e.g. events, replication controllers) on Kubemark master, which takes
a lot of time. Such work aren't needed in most cases: if you delete your
Kubemark cluster after running run-e2e-tests.sh; you don't care about
namespace deletion performance, specifically related to etcd; etc. There is a
flag that enables you to avoid namespace deletion: --delete-namespace=false.
Adding the flag should let you see in logs: Found DeleteNamespace=false, skipping namespace deletion!
Run-e2e-tests prints the same output on Kubemark as on ordinary e2e cluster, but if you need to dig deeper you need to learn how to debug HollowNodes and how Master machine (currently) differs from the ordinary one.
If you need to debug master machine you can do similar things as you do on your
ordinary master. The difference between Kubemark setup and ordinary setup is
that in Kubemark etcd is run as a plain docker container, and all master
components are run as normal processes. There’s no Kubelet overseeing them. Logs
are stored in exactly the same place, i.e. /var/logs/ directory. Because
binaries are not supervised by anything they won't be restarted in the case of a
crash.
To help you with debugging from inside the cluster startup script puts a
~/configure-kubectl.sh script on the master. It downloads gcloud and
kubectl tool and configures kubectl to work on unsecured master port (useful
if there are problems with security). After the script is run you can use
kubectl command from the master machine to play with the cluster.
Debugging HollowNodes is a bit more tricky, as if you experience a problem on
one of them you need to learn which hollow-node pod corresponds to a given
HollowNode known by the Master. During self-registeration HollowNodes provide
their cluster IPs as Names, which means that if you need to find a HollowNode
named 10.2.4.5 you just need to find a Pod in external cluster with this
cluster IP. There’s a helper script
test/kubemark/get-real-pod-for-hollow-node.sh that does this for you.
When you have a Pod name you can use kubectl logs on external cluster to get
logs, or use a kubectl describe pod call to find an external Node on which
this particular HollowNode is running so you can ssh to it.
E.g. you want to see the logs of HollowKubelet on which pod my-pod is running.
To do so you can execute:
$ kubectl kubernetes/test/kubemark/kubeconfig.kubemark describe pod my-pod
Which outputs pod description and among it a line:
Node: 1.2.3.4/1.2.3.4
To learn the hollow-node pod corresponding to node 1.2.3.4 you use
aforementioned script:
$ kubernetes/test/kubemark/get-real-pod-for-hollow-node.sh 1.2.3.4
which will output the line:
hollow-node-1234
Now you just use ordinary kubectl command to get the logs:
kubectl --namespace=kubemark logs hollow-node-1234
All those things should work exactly the same on all cloud providers.
On GCE you just need to execute test/kubemark/stop-kubemark.sh script, which
will delete HollowNode ReplicationController and all the resources for you. On
other providers you’ll need to delete all this stuff by yourself.
Kubemark master uses exactly the same binaries as ordinary Kubernetes does. This
means that it will never be out of date. On the other hand HollowNodes use
existing fake for Kubelet (called SimpleKubelet), which mocks its runtime
manager with pkg/kubelet/dockertools/fake_manager.go, where most logic sits.
Because there’s no easy way of mocking other managers (e.g. VolumeManager), they
are not supported in Kubemark (e.g. we can’t schedule Pods with volumes in them
yet).
As the time passes more fakes will probably be plugged into HollowNodes, but it’s crucial to make it as simple as possible to allow running a big number of Hollows on a single core.