断路器

本文中的这一任务展示了弹性应用的熔断能力。开发人员可以凭借这一能力,来限制因为故障、延迟高峰以及其他预计外的网络异常所造成的影响范围。下面将会演示如何针对连接、请求以及外部检测来进行断路器配置。

开始之前

kubectl apply -f <(istioctl kube-inject -f samples/httpbin/httpbin.yaml)

断路器

接下来设置一个场景来演示熔断能力。现在我们已经运行了httpbin服务。我们想要通过对istio目标策略的配置来设置一个熔断规则。在这之前首先要设置一个到这一目的的路由规则,这一规则会把所有访问httpbin的流量路由到version=v1去。

创建断路策略

  1. 创建缺省路由规则,让所有目标为httpbin的流量都指向v1

    istioctl create -f samples/httpbin/routerules/httpbin-v1.yaml
    
  2. 创建目标策略来对httpbin的调用过程进行断路设置。

    cat <<EOF | istioctl create -f -
    apiVersion: config.istio.io/v1beta1
    kind: DestinationPolicy
    metadata:
     name: httpbin-circuit-breaker
    spec:
     destination:
       name: httpbin
       labels:
         version: v1
     circuitBreaker:
       simpleCb:
         maxConnections: 1
         httpMaxPendingRequests: 1
         sleepWindow: 3m
         httpDetectionInterval: 1s
         httpMaxEjectionPercent: 100
         httpConsecutiveErrors: 1
         httpMaxRequestsPerConnection: 1
    EOF
    
  3. 确认目标策略是否正确创建

    istioctl get destinationpolicy
    
    NAME                    KIND                                            NAMESPACE
    httpbin-circuit-breaker DestinationPolicy.v1alpha2.config.istio.io      istio-samples
    

设置客户端

接下来我们来定义调用httpbin服务的规则。要创建一个客户端,用于向我们的服务发送流量,从而进一步体验断路器功能。我们会使用一个简单的负载测试工具fortio。使用这个客户端我们可以控制连接数量、并发数以及外发HTTP调用的延迟。这一步骤中,我们会设置一个客户端,注入istio sidecar,以此保证客户端的通信也在istio的监管之下:

kubectl apply -f <(istioctl kube-inject -f samples/httpbin/sample-client/fortio-deploy.yaml)

这样我们就能够登入客户端 Pod,并使用fortio工具来调用httpbin,使用-curl开关可以指定我们只执行一次调用。

FORTIO_POD=$(kubectl get pod | grep fortio | awk '{ print $1 }')
kubectl exec -it $FORTIO_POD  -c fortio /usr/local/bin/fortio -- load -curl  http://httpbin:8000/get

HTTP/1.1 200 OK
server: envoy
date: Tue, 16 Jan 2018 23:47:00 GMT
content-type: application/json
access-control-allow-origin: *
access-control-allow-credentials: true
content-length: 445
x-envoy-upstream-service-time: 36

{
  "args": {},
  "headers": {
    "Content-Length": "0",
    "Host": "httpbin:8000",
    "User-Agent": "istio/fortio-0.6.2",
    "X-B3-Sampled": "1",
    "X-B3-Spanid": "824fbd828d809bf4",
    "X-B3-Traceid": "824fbd828d809bf4",
    "X-Ot-Span-Context": "824fbd828d809bf4;824fbd828d809bf4;0000000000000000",
    "X-Request-Id": "1ad2de20-806e-9622-949a-bd1d9735a3f4"
  },
  "origin": "127.0.0.1",
  "url": "http://httpbin:8000/get"
}

这里可以看到,调用成功了!接下来我们试试熔断功能。

测试断路器

在断路器设置中,我们指定maxConnections: 1以及httpMaxPendingRequests: 1。这样的设置下,如果我们并发超过一个连接和请求,istio-proxy就会断掉后续的请求和连接。我们试试两个并发链接(-c 2),发送20个请求(-n 20):

kubectl exec -it $FORTIO_POD  -c fortio /usr/local/bin/fortio -- load -c 2 -qps 0 -n 20 -loglevel Warning http://httpbin:8000/get

Fortio 0.6.2 running at 0 queries per second, 2->2 procs, for 5s: http://httpbin:8000/get
Starting at max qps with 2 thread(s) [gomax 2] for exactly 20 calls (10 per thread + 0)
23:51:10 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
Ended after 106.474079ms : 20 calls. qps=187.84
Aggregated Function Time : count 20 avg 0.010215375 +/- 0.003604 min 0.005172024 max 0.019434859 sum 0.204307492
# range, mid point, percentile, count
>= 0.00517202 <= 0.006 , 0.00558601 , 5.00, 1
> 0.006 <= 0.007 , 0.0065 , 20.00, 3
> 0.007 <= 0.008 , 0.0075 , 30.00, 2
> 0.008 <= 0.009 , 0.0085 , 40.00, 2
> 0.009 <= 0.01 , 0.0095 , 60.00, 4
> 0.01 <= 0.011 , 0.0105 , 70.00, 2
> 0.011 <= 0.012 , 0.0115 , 75.00, 1
> 0.012 <= 0.014 , 0.013 , 90.00, 3
> 0.016 <= 0.018 , 0.017 , 95.00, 1
> 0.018 <= 0.0194349 , 0.0187174 , 100.00, 1
# target 50% 0.0095
# target 75% 0.012
# target 99% 0.0191479
# target 99.9% 0.0194062
Code 200 : 19 (95.0 %)
Code 503 : 1 (5.0 %)
Response Header Sizes : count 20 avg 218.85 +/- 50.21 min 0 max 231 sum 4377
Response Body/Total Sizes : count 20 avg 652.45 +/- 99.9 min 217 max 676 sum 13049
All done 20 calls (plus 0 warmup) 10.215 ms avg, 187.8 qps

会看到几乎所有请求都通过了。

Code 200 : 19 (95.0 %)
Code 503 : 1 (5.0 %)

这是因为istio-proxy允许一定的误差。我们把连接数提高到3:

kubectl exec -it $FORTIO_POD  -c fortio /usr/local/bin/fortio -- load -c 3 -qps 0 -n 20 -loglevel Warning http://httpbin:8000/get

Fortio 0.6.2 running at 0 queries per second, 2->2 procs, for 5s: http://httpbin:8000/get
Starting at max qps with 3 thread(s) [gomax 2] for exactly 30 calls (10 per thread + 0)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
23:51:51 W http.go:617> Parsed non ok code 503 (HTTP/1.1 503)
Ended after 71.05365ms : 30 calls. qps=422.22
Aggregated Function Time : count 30 avg 0.0053360199 +/- 0.004219 min 0.000487853 max 0.018906468 sum 0.160080597
# range, mid point, percentile, count
>= 0.000487853 <= 0.001 , 0.000743926 , 10.00, 3
> 0.001 <= 0.002 , 0.0015 , 30.00, 6
> 0.002 <= 0.003 , 0.0025 , 33.33, 1
> 0.003 <= 0.004 , 0.0035 , 40.00, 2
> 0.004 <= 0.005 , 0.0045 , 46.67, 2
> 0.005 <= 0.006 , 0.0055 , 60.00, 4
> 0.006 <= 0.007 , 0.0065 , 73.33, 4
> 0.007 <= 0.008 , 0.0075 , 80.00, 2
> 0.008 <= 0.009 , 0.0085 , 86.67, 2
> 0.009 <= 0.01 , 0.0095 , 93.33, 2
> 0.014 <= 0.016 , 0.015 , 96.67, 1
> 0.018 <= 0.0189065 , 0.0184532 , 100.00, 1
# target 50% 0.00525
# target 75% 0.00725
# target 99% 0.0186345
# target 99.9% 0.0188793
Code 200 : 19 (63.3 %)
Code 503 : 11 (36.7 %)
Response Header Sizes : count 30 avg 145.73333 +/- 110.9 min 0 max 231 sum 4372
Response Body/Total Sizes : count 30 avg 507.13333 +/- 220.8 min 217 max 676 sum 15214
All done 30 calls (plus 0 warmup) 5.336 ms avg, 422.2 qps

这样就看到,断路器开始发挥作用了:

Code 200 : 19 (63.3 %)
Code 503 : 11 (36.7 %)

只有63%的请求通过了,其他的都被断路器拒之门外,我们可以查询一下istio-proxy的统计数据:

kubectl exec -it $FORTIO_POD  -c istio-proxy  -- sh -c 'curl localhost:15000/stats' | grep httpbin | grep pending

cluster.out.httpbin.springistio.svc.cluster.local|http|version=v1.upstream_rq_pending_active: 0
cluster.out.httpbin.springistio.svc.cluster.local|http|version=v1.upstream_rq_pending_failure_eject: 0
cluster.out.httpbin.springistio.svc.cluster.local|http|version=v1.upstream_rq_pending_overflow: 12
cluster.out.httpbin.springistio.svc.cluster.local|http|version=v1.upstream_rq_pending_total: 39

upstream_rq_pending_overflow的值为12,说明有12次调用被断路器拦截了。

清理

  1. 清除规则。

    istioctl delete routerule httpbin-default-v1
    istioctl delete destinationpolicy httpbin-circuit-breaker
    
  2. 关闭httpbin服务和客户端。

    kubectl delete deploy httpbin fortio-deploy
    kubectl delete svc httpbin
    

下一步

阅读目标策略参考,其中会有更详尽的断路器相关内容。