Access network when scaling in TiKV node

Bug Report

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1. What did you do?

2020-06-18T08:41:35.841+0800	INFO	Execute command finished	{"code": 1, "error": "init config failed: 192.101.11.238:4000: fetch /timestamp.json from mirror(https://tiup-mirrors.pingcap.com/) failed: download from https://tiup-mirrors.pingcap.com/timestamp.json failed: Get https://tiup-mirrors.pingcap.com/timestamp.json: dial tcp: lookup tiup-mirrors.pingcap.com on [::1]:53: read udp [::1]:53941->[::1]:53: read: connection refused", "errorVerbose": "Get https://tiup-mirrors.pingcap.com/timestamp.json: dial tcp: lookup tiup-mirrors.pingcap.com on [::1]:53: read udp [::1]:53941->[::1]:53: read: connection refused\ndownload from https://tiup-mirrors.pingcap.com/timestamp.json failed\ngithub.com/pingcap/tiup/pkg/repository.(*httpMirror).download\n\tgithub.com/pingcap/tiup@/pkg/repository/mirror.go:219\ngithub.com/pingcap/tiup/pkg/repository.(*httpMirror).Fetch\n\tgithub.com/pingcap/tiup@/pkg/repository/mirror.go:256\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).fetchBase\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:527\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).fetchManifest\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:504\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).fetchTimestamp\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:462\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).updateLocalSnapshot\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:234\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).ensureManifests\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:180\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).FetchComponentManifest\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:624\ngithub.com/pingcap/tiup/pkg/repository.(*V1Repository).ComponentVersion\n\tgithub.com/pingcap/tiup@/pkg/repository/v1_repository.go:634\ngithub.com/pingcap/tiup/pkg/cluster/clusterutil.(*repositoryT).ComponentBinEntry\n\tgithub.com/pingcap/tiup@/pkg/cluster/clusterutil/cluster.go:91\ngithub.com/pingcap/tiup/pkg/cluster/meta.checkConfig\n\tgithub.com/pingcap/tiup@/pkg/cluster/meta/server_config.go:164\ngithub.com/pingcap/tiup/pkg/cluster/meta.(*TiDBInstance).InitConfig\n\tgithub.com/pingcap/tiup@/pkg/cluster/meta/logic.go:438\ngithub.com/pingcap/tiup/pkg/cluster/task.(*InitConfig).Execute\n\tgithub.com/pingcap/tiup@/pkg/cluster/task/init_config.go:46\ngithub.com/pingcap/tiup/pkg/cluster/task.(*Serial).Execute\n\tgithub.com/pingcap/tiup@/pkg/cluster/task/task.go:183\ngithub.com/pingcap/tiup/pkg/cluster/task.(*Parallel).Execute.func1\n\tgithub.com/pingcap/tiup@/pkg/cluster/task/task.go:236\nruntime.goexit\n\truntime/asm_amd64.s:1357\nfetch /timestamp.json from mirror(https://tiup-mirrors.pingcap.com/) failed\ninit config failed: 192.101.11.238:4000"}

Start with the scaling-related call path in pkg/cluster/meta/logic.go and pkg/cluster/meta/server_config.go, then trace the mirror access through pkg/repository/mirror.go and the repository files named in the stack trace. First reproduce the TiKV scaling operation with the shown DNS failure and determine the expected behavior when the mirror cannot be reached. Done means the failure mode is understood and the scaling path has verified handling for it.