在 Kubernetes 裡跑 curl 來測試內部服務

有時會需要測試架在 Kubernetes service 裡的內部網站，

比如說像 https://eck-es-master.svc.cluster.local:9200 這種網址，

在叢集外面是不能存取的。

當然你可以選擇用 port-forward 的方式來存取，

另一種方法就是直接在 K8S 叢集裡跑 curl 囉～

執行下面的指令，來建立一個 curl 的 pod 並進入 shell：
```
kubectl run curl --image=curlimages/curl -it -- sh
```

接著就可以在裡面打 curl 指令測試囉：
```
$ curl -L -v https://eck-es-master.svc.cluster.local:9200
*   Trying 10.1.9.70:9200...
* Connected to eck-es-master.ssb-elasticsearch.svc.cluster.local (10.1.9.70) port 9200 (#0)
* ALPN: offers h2
* ALPN: offers http/1.1
*  CAfile: /cacert.pem
*  CApath: none
* [CONN-0-0][CF-SSL] TLSv1.3 (OUT), TLS handshake, Client hello (1):
* [CONN-0-0][CF-SSL] TLSv1.3 (IN), TLS handshake, Server hello (2):
* [CONN-0-0][CF-SSL] TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
* [CONN-0-0][CF-SSL] TLSv1.3 (IN), TLS handshake, Certificate (11):
* [CONN-0-0][CF-SSL] TLSv1.3 (OUT), TLS alert, unknown CA (560):
* SSL certificate problem: unable to get local issuer certificate
* Closing connection 0
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.se/docs/sslcerts.html
curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.
```

如果已經退出了這個 pod，因為我沒有加  `--rm` 選項，

所以可以隨時  `kubectl exec -it curl -- sh` 進這個 pod 再來測試囉～