Autoscale Sample App - Go¶
A demonstration of the autoscaling capabilities of a Knative Serving Revision.
Prerequisites¶
- A Kubernetes cluster with Knative Serving installed.
- The
heyload generator installed (go get -u github.com/rakyll/hey). - Clone this repository, and move into the sample directory:
git clone -b "v0.23.0" https://github.com/knative/docs knative-docs
cd knative-docs
Deploy the Service¶
- Deploy the sample Knative Service:
kubectl apply --filename docs/serving/autoscaling/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.devwhich is the concurrency-based autoscaler described above (the default), andhpa.autoscaling.knative.devwhich 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, the
autoscaling.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/autoscaling/autoscale-go/service.yaml