英文:
Kubernetes internal hostname is resolved to localhost
问题
我正在尝试使用内部服务 DNS 进行服务间的 HTTP 通信。
如果我尝试从另一个部署的 Pod 中使用 curl 访问一个 Pod，它是可以工作的，但是在使用 golang 的 net/http 服务时无法使用。
当进行 API 调用时，hydra-admin.microservices.svc.cluster.local 解析为 localhost，但是如下所示，curl 是可以工作的。
/ # curl -X PUT http://hydra-admin:4445/admin/oauth2/auth/requests/login/accept?login_challenge=6f51146e49c54b739de8a37b25a72349
{"error":"invalid_request","error_description":"The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed. Unable to decode body because: EOF"}
我在这里漏掉了什么？
英文:
I'm trying to use internal service DNS for service-to-service HTTP communication.
If I try to curl a pod from another deployment pod it is working but unable to use it in golang net/http service
2023/01/27 15:48:37 oauth2.go:90: oauth2 url http://hydra-admin.microservices.svc.cluster.local:4445/oauth2/auth/requests/login/accept
2023/01/27 15:48:37 oauth2.go:101: Unable to make http request Put "http://localhost:4445/admin/oauth2/auth/requests/login/accept?login_challenge=b569006c8b834a298cf1cd72e2424953": dial tcp [::1]:4445: connect: connection refused
hydra-admin.microservices.svc.cluster.local is resolved to localhost when the API call is made
but curl works as you see below
/ # curl -X PUT http://hydra-admin:4445/admin/oauth2/auth/requests/login/accept?login_challenge=6f51146e49c54b739de8a37b25a72349
{"error":"invalid_request","error_description":"The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed. Unable to decode body because: EOF"}
What am I missing here?
答案1
得分: 1
根据我的评论，根据您构建go可执行文件的方式，它在k8s环境中的行为会有所不同。您是使用scratch镜像还是CGO_ENABLED=1镜像？
根据dns包的文档，有关DNS行为的一个注意事项如下：
默认情况下，使用纯Go解析器，因为阻塞的DNS请求只消耗一个goroutine，而阻塞的C调用则会消耗一个操作系统线程。当cgo可用时，在以下各种条件下将使用基于cgo的解析器：
...当/etc/resolv.conf或/etc/nsswitch.conf指定使用Go解析器未实现的功能，并且要查找的名称以.local结尾或是mDNS名称时。
因此，我建议您为k8s构建您的go可执行文件，以最大化外部和内部DNS请求的成功率，方法如下：
CGO_ENABLED=1 go build -tags netgo
英文:
Per my comment, depending on how you are building your go executable will have an effect on how it behaves within a k8s environment. Are you using a scratch image or a CGO_ENABLED=1 image?
From the dns package docs there's a caveat on DNS behavior
> By default the pure Go resolver is used, because a blocked DNS request
> consumes only a goroutine, while a blocked C call consumes an
> operating system thread. When cgo is available, the cgo-based resolver
> is used instead under a variety of conditions:
> ... when /etc/resolv.conf or /etc/nsswitch.conf specify the use of features
> that the Go resolver does not implement, and when the name being
> looked up ends in .local or is an mDNS name.
So I would suggest - to maximized your success rate for both external & internal DNS requests - building your go executable for k8s like so:
CGO_ENABLED=1 go build -tags netgo
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