.github: add external link check

.github/workflows/ci.yaml

@@ -22,9 +22,9 @@ jobs:
       with:
         config: './.markdownlint.yaml'
         args: '.'
-    - name: Verify links
+    - name: Verify internal links
       run: ./hack/verify-links.sh
-    - name: Verify link anchors
+    - name: Verify internal link anchors
       run: ./hack/verify-link-anchors.sh 
     - name: "Check unclosed tags"
       run: 

.github/workflows/link-check.yaml

@@ -0,0 +1,37 @@
+name: external-link-check
+
+on: [pull_request]
+
+jobs:
+  base:
+    runs-on: ubuntu-18.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+
+      # NOTE:
+      #  - the check process can be very fast,
+      #    but if `-c` is too large then `Too Many Requests (HTTP error 429)` may be reported from `https://github.com/*`.
+      #  - we hardcode `--document-root` to `/github/workspace` in the container now.
+      #  - we use `http://172.*` as sample addresses in some docs, so we need to exclude them.
+      - name: Check external links in zh files
+        id: lczh
+        uses: peter-evans/link-checker@v1
+        with:
+          args: -c 32 -d /github/workspace -r -x "http://172.*|https://github.com/.*/pull/.*|https://github.com/.*/issues/.*|https://github.com/[^.\n]*$|http://127.0.0.1.*|http://localhost.*|.*.md" zh*
+
+      - name: Check external links in en files
+        id: lcen
+        uses: peter-evans/link-checker@v1
+        with:
+          args: -c 32 -d /github/workspace -r -x "http://172.*|https://github.com/.*/pull/.*|https://github.com/.*/issues/.*|https://github.com/[^.\n]*$|http://127.0.0.1.*|http://localhost.*|.*.md" en*
+
+      - name: Fail if there were external link errors
+        if: ${{ steps.lczh.outputs.exit_code || steps.lcen.outputs.exit_code }}
+        run: |
+          echo "Please check the broken links reported in previous steps \"Check external links in zh files\" and \"Check external links in en files\"."
+          exit ${{ steps.lczh.outputs.exit_code || steps.lcen.outputs.exit_code }}
+      # Debug via SSH if previous steps failed
+      #- name: Set up tmate session
+      #  if: ${{ failure() }}
+      #  uses: mxschmitt/action-tmate@v2

en/configure-a-tidb-cluster.md

@@ -386,7 +386,7 @@ spec:
       logLevel: info
 ```
 
-For all configurable start parameters of TiCDC, see [TiCDC start parameters](https://pingcap.com/docs/stable/ticdc/deploy-ticdc/#manually-add-ticdc-component-to-an-existing-tidb-cluster).
+For all configurable start parameters of TiCDC, see [TiCDC configuration](https://github.com/pingcap/tidb-operator/blob/master/docs/api-references/docs.md#ticdcconfig).
 
 ## Configure high availability
 

en/enable-admission-webhook.md

@@ -12,7 +12,7 @@ Kubernetes v1.9 introduces the [dynamic admission control](https://kubernetes.io
 
 Unlike those of most products on Kubernetes, the admission controller of TiDB Operator consists of two mechanisms: [extension API-server](https://kubernetes.io/docs/tasks/access-kubernetes-api/setup-extension-api-server/) and [Webhook Configuration](https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#configure-admission-webhooks-on-the-fly).
 
-To use the admission controller, you need to enable the aggregation layer feature of the Kubernetes cluster. The feature is enabled by default. To check whether it is enabled, see [Enable Kubernetes Apiserver flags](https://kubernetes.io/docs/tasks/access-kubernetes-api/configure-aggregation-layer/#enable-kubernetes-apiserver-flags).
+To use the admission controller, you need to enable the aggregation layer feature of the Kubernetes cluster. The feature is enabled by default. To check whether it is enabled, see [Enable Kubernetes Apiserver flags](https://kubernetes.io/docs/tasks/extend-kubernetes/configure-aggregation-layer/#enable-kubernetes-apiserver-flags).
 
 ## Enable the admission controller
 

zh/configure-a-tidb-cluster.md

@@ -366,7 +366,7 @@ spec:
       logLevel: info
 ```
 
-获取所有可以配置的 TiCDC 启动参数，请参考 [TiCDC 启动参数文档](https://pingcap.com/docs-cn/stable/ticdc/deploy-ticdc/#手动在原有-tidb-集群上新增-ticdc-组件)。
+获取所有可以配置的 TiCDC 启动参数，请参考 [TiCDC 启动参数文档](https://github.com/pingcap/tidb-operator/blob/master/docs/api-references/docs.md#ticdcconfig)。
 
 ## 高可用配置
 

zh/enable-admission-webhook.md

@@ -10,7 +10,7 @@ Kubernetes 在 1.9 版本引入了 [动态准入机制](https://kubernetes.io/zh
 
 ## 先置条件
 
-TiDB Operator 准入控制器与大部分 Kubernetes 平台上产品的准入控制器较为不同，TiDB Operator 通过[扩展 API-Server](https://kubernetes.io/docs/tasks/access-kubernetes-api/setup-extension-api-server/) 与 [WebhookConfiguration](https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#configure-admission-webhooks-on-the-fly) 的两个机制组合而成。所以需要 Kubernetes 集群启用聚合层功能，通常情况下这个功能已经默认开启。如需查看是否开启聚合层功能，请参考[启用 Kubernetes Apiserver 标志](https://kubernetes.io/zh/docs/tasks/access-kubernetes-api/configure-aggregation-layer/#%E5%90%AF%E7%94%A8-kubernetes-apiserver-%E6%A0%87%E5%BF%97)。
+TiDB Operator 准入控制器与大部分 Kubernetes 平台上产品的准入控制器较为不同，TiDB Operator 通过[扩展 API-Server](https://kubernetes.io/docs/tasks/access-kubernetes-api/setup-extension-api-server/) 与 [WebhookConfiguration](https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#configure-admission-webhooks-on-the-fly) 的两个机制组合而成。所以需要 Kubernetes 集群启用聚合层功能，通常情况下这个功能已经默认开启。如需查看是否开启聚合层功能，请参考[启用 Kubernetes Apiserver 标志](https://kubernetes.io/zh/docs/tasks/extend-kubernetes/configure-aggregation-layer/#启用-kubernetes-apiserver-标志)。
 
 ## 开启 TiDB Operator 准入控制器
 
@@ -169,7 +169,7 @@ TiDB Operator 在默认安装情况下不会开启准入控制器，你需要手
 4. 修改 values.yaml 并安装或升级 TiDB Operator
 
     获取 `ca.crt` 的值：
-    
+
     {{< copyable "shell-regular" >}}
 
     ```shell
@@ -217,7 +217,7 @@ TiDB Operator 通过准入控制器的帮助实现了许多功能。我们将在
     {{< copyable "shell-regular" >}}
 
     ```shell
-    $  kubectl annotate tidbcluster ${name} -n ${namespace} tidb.pingcap.com/tikv-partition=2 
+    $  kubectl annotate tidbcluster ${name} -n ${namespace} tidb.pingcap.com/tikv-partition=2
     tidbcluster.pingcap.com/${name} annotated
     ```
 
@@ -226,7 +226,7 @@ TiDB Operator 通过准入控制器的帮助实现了许多功能。我们将在
     {{< copyable "shell-regular" >}}
 
     ```shell
-    $  kubectl annotate tidbcluster ${name} -n ${namespace} tidb.pingcap.com/tikv-partition- 
+    $  kubectl annotate tidbcluster ${name} -n ${namespace} tidb.pingcap.com/tikv-partition-
     tidbcluster.pingcap.com/${name} annotated
     ```