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Autoscale Sample App - Go
A demonstration of the autoscaling capabilities of a Knative Serving Revision.
Prerequisites
-
A Kubernetes cluster with Knative Serving installed.
-
The
hey
load generator installed (go get -u github.com/rakyll/hey
). -
Clone this repository, and move into the sample directory:
git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs cd knative-docs
Deploy the Service
-
Deploy the sample Knative Service:
kubectl apply --filename docs/serving/samples/autoscale-go/service.yaml
-
Obtain the URL of the service (once
Ready
):$ kubectl get ksvc autoscale-go NAME URL LATESTCREATED LATESTREADY READY REASON autoscale-go http://autoscale-go.default.1.2.3.4.xip.io autoscale-go-96dtk autoscale-go-96dtk True
Load the Service
-
Make a request to the autoscale app to see it consume some resources.
curl "http://autoscale-go.default.1.2.3.4.xip.io?sleep=100&prime=10000&bloat=5"
Allocated 5 Mb of memory. The largest prime less than 10000 is 9973. Slept for 100.13 milliseconds.
-
Send 30 seconds of traffic maintaining 50 in-flight requests.
hey -z 30s -c 50 \ "http://autoscale-go.default.1.2.3.4.xip.io?sleep=100&prime=10000&bloat=5" \ && kubectl get pods
Summary: Total: 30.3379 secs Slowest: 0.7433 secs Fastest: 0.1672 secs Average: 0.2778 secs Requests/sec: 178.7861 Total data: 542038 bytes Size/request: 99 bytes Response time histogram: 0.167 [1] | 0.225 [1462] |■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 0.282 [1303] |■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 0.340 [1894] |■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 0.398 [471] |■■■■■■■■■■ 0.455 [159] |■■■ 0.513 [68] |■ 0.570 [18] | 0.628 [14] | 0.686 [21] | 0.743 [13] | Latency distribution: 10% in 0.1805 secs 25% in 0.2197 secs 50% in 0.2801 secs 75% in 0.3129 secs 90% in 0.3596 secs 95% in 0.4020 secs 99% in 0.5457 secs Details (average, fastest, slowest): DNS+dialup: 0.0007 secs, 0.1672 secs, 0.7433 secs DNS-lookup: 0.0000 secs, 0.0000 secs, 0.0000 secs req write: 0.0001 secs, 0.0000 secs, 0.0045 secs resp wait: 0.2766 secs, 0.1669 secs, 0.6633 secs resp read: 0.0002 secs, 0.0000 secs, 0.0065 secs Status code distribution: [200] 5424 responses
NAME READY STATUS RESTARTS AGE autoscale-go-00001-deployment-78cdc67bf4-2w4sk 3/3 Running 0 26s autoscale-go-00001-deployment-78cdc67bf4-dd2zb 3/3 Running 0 24s autoscale-go-00001-deployment-78cdc67bf4-pg55p 3/3 Running 0 18s autoscale-go-00001-deployment-78cdc67bf4-q8bf9 3/3 Running 0 1m autoscale-go-00001-deployment-78cdc67bf4-thjbq 3/3 Running 0 26s
Analysis
Algorithm
Knative Serving autoscaling is based on the average number of in-flight requests
per pod (concurrency). The system has a default
target concurrency of 100(Search for container-concurrency-target-default)
but we used 10 for our service. We loaded the service
with 50 concurrent requests so the autoscaler created 5 pods
(50 concurrent requests / target of 10 = 5 pods
)
Panic
The autoscaler calculates average concurrency over a 60 second window so it
takes a minute for the system to stablize at the desired level of concurrency.
However the autoscaler also calculates a 6 second panic
window and will enter
panic mode if that window reached 2x the target concurrency. In panic mode the
autoscaler operates on the shorter, more sensitive panic window. Once the panic
conditions are no longer met for 60 seconds, the autoscaler will return to the
initial 60 second stable
window.
|
Panic Target---> +--| 20
| |
| <------Panic Window
| |
Stable Target---> +-------------------------|--| 10 CONCURRENCY
| | |
| <-----------Stable Window
| | |
--------------------------+-------------------------+--+ 0
120 60 0
TIME
Customization
The autoscaler supports customization through annotations. There are two autoscaler classes built into Knative:
-
kpa.autoscaling.knative.dev
which is the concurrency-based autoscaler described above (the default), and -
hpa.autoscaling.knative.dev
which delegates to the Kubernetes HPA which autoscales on CPU usage.Example of a Service scaled on CPU:
apiVersion: serving.knative.dev/v1 kind: Service metadata: name: autoscale-go namespace: default spec: template: metadata: annotations: # Standard Kubernetes CPU-based autoscaling. autoscaling.knative.dev/class: hpa.autoscaling.knative.dev autoscaling.knative.dev/metric: cpu spec: containers: - image: gcr.io/knative-samples/autoscale-go:0.1
Additionally the autoscaler targets and scaling bounds can be specified in annotations. Example of a Service with custom targets and scale bounds:
apiVersion: serving.knative.dev/v1 kind: Service metadata: name: autoscale-go namespace: default spec: template: metadata: annotations: # Knative concurrency-based autoscaling (default). autoscaling.knative.dev/class: kpa.autoscaling.knative.dev autoscaling.knative.dev/metric: concurrency # Target 10 requests in-flight per pod. autoscaling.knative.dev/target: "10" # Disable scale to zero with a minScale of 1. autoscaling.knative.dev/minScale: "1" # Limit scaling to 100 pods. autoscaling.knative.dev/maxScale: "100" spec: containers: - image: gcr.io/knative-samples/autoscale-go:0.1
Note: for an
hpa.autoscaling.knative.dev
class service, theautoscaling.knative.dev/target
specifies the CPU percentage target (default"80"
).
Demo
View the Kubecon Demo of Knative autoscaler customization (32 minutes).
Other Experiments
-
Send 60 seconds of traffic maintaining 100 concurrent requests.
hey -z 60s -c 100 \ "http://autoscale-go.default.1.2.3.4.xip.io?sleep=100&prime=10000&bloat=5"
-
Send 60 seconds of traffic maintaining 100 qps with short requests (10 ms).
hey -z 60s -q 100 \ "http://autoscale-go.default.1.2.3.4.xip.io?sleep=10"
-
Send 60 seconds of traffic maintaining 100 qps with long requests (1 sec).
hey -z 60s -q 100 \ "http://autoscale-go.default.1.2.3.4.xip.io?sleep=1000"
-
Send 60 seconds of traffic with heavy CPU usage (~1 cpu/sec/request, total 100 cpus).
hey -z 60s -q 100 \ "http://autoscale-go.default.1.2.3.4.xip.io?prime=40000000"
-
Send 60 seconds of traffic with heavy memory usage (1 gb/request, total 5 gb).
hey -z 60s -c 5 \ "http://autoscale-go.default.1.2.3.4.xip.io?bloat=1000"
Cleanup
kubectl delete --filename docs/serving/samples/autoscale-go/service.yaml
Further reading
Autoscaling Developer Documentation
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