Alpine Linux添加Let's Encrypt CA證書或者自籤CA證書
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1. 用docker進行查看
進入容器，docker run -it alpine:latest /bin/sh
安裝curl，apk --no-cache add curl
對比發現curl依賴ca-certificates，
網上查到update-ca-certificates命令爲更新系統ca證書，
2. 添加CA證書
經過操作總結，發現有2種方式添加ca證書至系統內，以下示例：
2.1 放至目錄/usr/local/share/ca-certificates/
將Let's Encrypt Authority X3的CA證書Letsencrypt_Root_CA.crt放至目錄/usr/local/share/ca-certificates/下，並執行update-ca-certificates，即可完成證書更新。
-----BEGIN CERTIFICATE-----
MIIEkjCCA3qgAwIBAgIQCgFBQgAAAVOFc2oLheynCDANBgkqhkiG9w0BAQsFADA/
MSQwIgYDVQQKExtEaWdpdGFsIFNpZ25hdHVyZSBUcnVzdCBDby4xFzAVBgNVBAMT
DkRTVCBSb290IENBIFgzMB4XDTE2MDMxNzE2NDA0NloXDTIxMDMxNzE2NDA0Nlow
SjELMAkGA1UEBhMCVVMxFjAUBgNVBAoTDUxldCdzIEVuY3J5cHQxIzAhBgNVBAMT
GkxldCdzIEVuY3J5cHQgQXV0aG9yaXR5IFgzMIIBIjANBgkqhkiG9w0BAQEFAAOC
AQ8AMIIBCgKCAQEAnNMM8FrlLke3cl03g7NoYzDq1zUmGSXhvb418XCSL7e4S0EF
q6meNQhY7LEqxGiHC6PjdeTm86dicbp5gWAf15Gan/PQeGdxyGkOlZHP/uaZ6WA8
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AQH/BAgwBgEB/wIBADAOBgNVHQ8BAf8EBAMCAYYwfwYIKwYBBQUHAQEEczBxMDIG
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Y3JsMB0GA1UdDgQWBBSoSmpjBH3duubRObemRWXv86jsoTANBgkqhkiG9w0BAQsF
AAOCAQEA3TPXEfNjWDjdGBX7CVW+dla5cEilaUcne8IkCJLxWh9KEik3JHRRHGJo
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X4Po1QYz+3dszkDqMp4fklxBwXRsW10KXzPMTZ+sOPAveyxindmjkW8lGy+QsRlG
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KOqkqm57TH2H3eDJAkSnh6/DNFu0Qg==
-----END CERTIFICATE-----
2.2 放至目錄/usr/share/ca-certificates/
將Let's Encrypt Authority X3的CA證書Letsencrypt_Root_CA.crt放至目錄/usr/share/ca-certificates/下，在文件/etc/ca-certificates.conf中配置引用路徑，並執行update-ca-certificates，即可完成證書更新。
3. 小結
從curl命令過程可以看出，/etc/ssl/certs/ca-certificates.crt是最終生效的CA文件，因此，可以將CA證書的內容直接添加進此文件。update-ca-certificates其實也就是乾的這件事，在沒有此命令時，直接添加內容至CA文件中是最好的選擇。
以下是gitlab-runner不支持letsencrypt證書解決辦法：
Dockerfile
FROM gitlab/gitlab-runner:alpine-v11.11.2
USER root
COPY Letsencrypt_Root_CA.crt /usr/local/share/ca-certificates/
RUN apk --no-cache add ca-certificates \
&& rm -rf /var/cache/apk/* \
&& update-ca-certificates
USER gitlab-runner