8.7　重试

Istio通过设置VirtualService中的retries字段来指定服务的重试机制。

使用示例如下：

1 apiVersion: networking.istio.io/v1alpha3
 2 kind: VirtualService
 3 metadata:
 4   name: service-node
 5 spec:
 6   hosts:
 7   - service-node
 8   http:
 9   - route:
10     - destination:
11         host: service-node
12     retries:
13       attempts: 3
14       perTryTimeout: 2s

第12~14行定义了重试规则，当调用service-node服务时，如果服务出错，就需要进行重试，最多可以重试3次，每次调用超时为2秒，每次重试的时间间隔由Istio决定，重试时间间隔一般会大于25毫秒。

【实验】

1）创建并发测试的Pod：

$ kubectl apply -f kubernetes/fortio.yaml

2）部署httpbin服务：

$ kubectl apply -f kubernetes/httpbin.yaml
$ kubectl get pod -l app=httpbin
NAME                        READY     STATUS      RESTARTS     AGE
httpbin-b67975b8f-vmbtv     2/2       Running     0            49s

3）创建httpbin服务路由规则：

$ kubectl apply -f istio/route/virtual-service-httpbin.yaml

4）访问httpbin服务：

$ kubectl exec fortio -c fortio /usr/local/bin/fortio -- load -curl http://httpbin:8000/status/200
HTTP/1.1 200 OK
server: envoy
date: Wed, 16 Jan 2019 14:03:00 GMT
content-type: text/html; charset=utf-8
access-control-allow-origin: *
access-control-allow-credentials: true
content-length: 0
x-envoy-upstream-service-time: 33
$ kubectl exec fortio -c fortio /usr/local/bin/fortio -- load -c 10 -qps 0 -n 100 -loglevel Error http://httpbin:8000/status/200%2C200%2C200%2C200%2C500
14:18:37 I logger.go:97> Log level is now 4 Error (was 2 Info)
Fortio 1.0.1 running at 0 queries per second, 2->2 procs, for 100 calls: http://httpbin:8000/status/200%2C200%2C200%2C200%2C500
Aggregated Function Time : count 100 avg 0.24802899 +/- 0.06426 min 0.016759858 max 0.390472066 sum 24.8028985
# target 50% 0.252941
# target 75% 0.289706
# target 90% 0.326667
# target 99% 0.376981
# target 99.9% 0.389123
Sockets used: 30 (for perfect keepalive, would be 10)
Code 200 : 78 (78.0 %)
Code 500 : 22 (22.0 %)
All done 100 calls (plus 0 warmup) 248.029 ms avg, 38.5 qps

5）创建httpbin服务重试路由规则：

$ kubectl apply -f istio/resilience/virtual-service-httpbin-retry.yaml

6）访问httpbin服务：

$ kubectl exec fortio -c fortio /usr/local/bin/fortio -- load -curl http://httpbin:8000/status/200
HTTP/1.1 200 OK
server: envoy
date: Wed, 16 Jan 2019 14:19:14 GMT
content-type: text/html; charset=utf-8
access-control-allow-origin: *
access-control-allow-credentials: true
content-length: 0
x-envoy-upstream-service-time: 5
$ kubectl exec fortio -c fortio /usr/local/bin/fortio -- load -c 10 -qps 0 -n 100 -loglevel Error http://httpbin:8000/status/200%2C200%2C200%2C200%2C500
14:19:32 I logger.go:97> Log level is now 4 Error (was 2 Info)
Fortio 1.0.1 running at 0 queries per second, 2->2 procs, for 100 calls: http://httpbin:8000/status/200%2C200%2C200%2C200%2C500
Aggregated Function Time : count 100 avg 0.23708609 +/- 0.1323 min 0.017537636 max 0.793965189 sum 23.7086086
# target 50% 0.226471
# target 75% 0.275
# target 90% 0.383333
# target 99% 0.7
# target 99.9% 0.784569
Sockets used: 13 (for perfect keepalive, would be 10)
Code 200 : 97 (97.0 %)
Code 500 : 3 (3.0 %)
All done 100 calls (plus 0 warmup) 237.086 ms avg, 35.5 qps

从上面的测试结果可以看出，当没有开启服务重试时，服务有大概1/4的请求失败，当开启服务重试之后，服务只有极少数的请求失败。

7）清理：

$ kubectl delete -f kubernetes/fortio.yaml
$ kubectl delete -f kubernetes/httpbin.yaml
$ kubectl delete -f istio/resilience/virtual-service-httpbin-retry.yaml