k8s Podが標準出力に出したログは、どの様にEKSノード上のログファイルとして記録されるのか？

#はじめに
k8s Podが標準出力に出したログは、どの様にEKSノード上のログファイルとして記録されるのかのメモ。
WEBで調べて見たけれど余り情報が見当らなかっため、EKSクラスタ作って確認してみた。

#前提の環境
* kubernetes version:  1.20
* eksctl version: 0.62.0
* EKSノードはマネージド型ノードグループとして作成
* EKSノードのOS: AmazonLinux2/1.20

#ログディレクトリ階層、ファイル名
ディレクトリは大きく2つある模様。

##1. /var/log/containers
各Podのログのシンボリックリンクが張ってある。
ファイル名は #{Pod名}#{Namespace名}#{サービス名}-#{乱数？}.log

```
[root@ip-192-168-0-204 containers]# pwd
/var/log/containers
[root@ip-192-168-0-204 containers]# ll
total 0
lrwxrwxrwx 1 root root  92 Dec 14 03:13 aws-node-r78x8_kube-system_aws-node-44d7e9da5a56fa07c48e2bdc45aa084548fa6264b9a400387d4c4a4188122b20.log -> /var/log/pods/kube-system
_aws-node-r78x8_3e054baa-fecb-4e2f-a269-73124c95603b/aws-node/0.log
lrwxrwxrwx 1 root root 100 Dec 14 03:13 aws-node-r78x8_kube-system_aws-vpc-cni-init-a24558268ada64ab26ff14e159cf7b3010a8361726cadc4437c4dcd163f23db1.log -> /var/log/pods/kub
e-system_aws-node-r78x8_3e054baa-fecb-4e2f-a269-73124c95603b/aws-vpc-cni-init/0.log
lrwxrwxrwx 1 root root 101 Dec 14 03:13 coredns-54bc78bc49-662nj_kube-system_coredns-95f68db2920b5330a65dbeda2c5014474e0f26eb17066ec9a86582b92fe0fa04.log -> /var/log/pods/ku
be-system_coredns-54bc78bc49-662nj_295cc684-7a66-4c4b-ae97-5c728ba6593e/coredns/0.log
lrwxrwxrwx 1 root root  96 Dec 14 03:13 kube-proxy-9ccf5_kube-system_kube-proxy-4b44b5636b348fbb2f78d8160b40caeddc3bcc0617a9af168a929719d05c501c.log -> /var/log/pods/kube-sy
stem_kube-proxy-9ccf5_6b606d7f-e139-4b04-81cb-9cf81d39bb62/kube-proxy/0.log
lrwxrwxrwx 1 root root 113 Dec 14 04:00 linkerd-destination-56578b6779-g8zbx_linkerd_destination-245ef82fd72e3a651e6f18ef28d0db9faca7b0dbb8e7a0f782158db83639583c.log -> /var
/log/pods/linkerd_linkerd-destination-56578b6779-g8zbx_906680d6-0c01-4edb-8234-f51639980d1e/destination/0.log
lrwxrwxrwx 1 root root 114 Dec 14 04:00 linkerd-destination-56578b6779-g8zbx_linkerd_linkerd-init-454de82e2ee42cb3451eccdda6c8bea20a1d57d26b44ef496c48b7baaf39a147.log -> /va
r/log/pods/linkerd_linkerd-destination-56578b6779-g8zbx_906680d6-0c01-4edb-8234-f51639980d1e/linkerd-init/0.log
lrwxrwxrwx 1 root root 115 Dec 14 04:00 linkerd-destination-56578b6779-g8zbx_linkerd_linkerd-proxy-9eefba5eedf7d83d842393bc85fd5091aa0824a39e70f37c0f802c4ba0928706.log -> /v
ar/log/pods/linkerd_linkerd-destination-56578b6779-g8zbx_906680d6-0c01-4edb-8234-f51639980d1e/linkerd-proxy/0.log
lrwxrwxrwx 1 root root 117 Dec 14 04:00 linkerd-proxy-injector-7674b595d5-bpftr_linkerd_linkerd-init-f95bf5de058035dcbf3c6f904e4c8e231d8f42d5fa190fca47d8f0cbaec8beda.log -> 
/var/log/pods/linkerd_linkerd-proxy-injector-7674b595d5-bpftr_04183c88-0434-4afa-80d7-028326362101/linkerd-init/0.log
lrwxrwxrwx 1 root root 118 Dec 14 04:00 linkerd-proxy-injector-7674b595d5-bpftr_linkerd_linkerd-proxy-1352d4689479590f4f7b76b9f411c8def71efa1ce5e8f799d8c128d2d2a73caf.log ->
 /var/log/pods/linkerd_linkerd-proxy-injector-7674b595d5-bpftr_04183c88-0434-4afa-80d7-028326362101/linkerd-proxy/0.log
lrwxrwxrwx 1 root root 119 Dec 14 04:00 linkerd-proxy-injector-7674b595d5-bpftr_linkerd_proxy-injector-648674ba1b2d04c575c38183400c4722520c5047a009ff9a1cad64db831d4110.log -

/var/log/pods/linkerd_linkerd-proxy-injector-7674b595d5-bpftr_04183c88-0434-4afa-80d7-028326362101/proxy-injector/0.log
lrwxrwxrwx 1 root root 115 Dec 14 04:00 linkerd-sp-validator-5d7bb655ff-7rc45_linkerd_linkerd-init-b13957cebd22f3c463ab33c6b912677de6419c0a4c10f3188730796d208becf6.log -> /v
ar/log/pods/linkerd_linkerd-sp-validator-5d7bb655ff-7rc45_ba4033e6-2a0f-46de-9196-ed2922b4a0e2/linkerd-init/0.log
lrwxrwxrwx 1 root root 116 Dec 14 04:00 linkerd-sp-validator-5d7bb655ff-7rc45_linkerd_linkerd-proxy-43b35927841430cf894d67681cf59f5e30d4de73a0eb82ad3e2fcd02c9e2f525.log -> /
var/log/pods/linkerd_linkerd-sp-validator-5d7bb655ff-7rc45_ba4033e6-2a0f-46de-9196-ed2922b4a0e2/linkerd-proxy/0.log
lrwxrwxrwx 1 root root 115 Dec 14 04:00 linkerd-sp-validator-5d7bb655ff-7rc45_linkerd_sp-validator-84832e412886dcca3a6bfb4b62e56749850efeab439e0fead7e3328f9af0917f.log -> /v
ar/log/pods/linkerd_linkerd-sp-validator-5d7bb655ff-7rc45_ba4033e6-2a0f-46de-9196-ed2922b4a0e2/sp-validator/0.log
lrwxrwxrwx 1 root root  95 Dec 14 04:01 web-79469b946f-mdhhn_emojivoto_web-svc-d1854f07b48bed71480e80b3b070c6d6a652ba610185b231626eaee66ae694ac.log -> /var/log/pods/emojivot
o_web-79469b946f-mdhhn_c8feaa9b-152d-4d00-836b-61677f146179/web-svc/0.log
```


##2. /var/log/pods/#{Namespace名_Pod名_UUID}/#{サービス名}
上シンボリックリンクの実体
ファイル名は0.log

```
[root@ip-192-168-0-204 pods]# pwd
/var/log/pods
[root@ip-192-168-0-204 pods]# ll
total 0
drwxr-xr-x 3 root root 21 Dec 14 04:01 emojivoto_web-79469b946f-mdhhn_c8feaa9b-152d-4d00-836b-61677f146179
drwxr-xr-x 4 root root 46 Dec 14 03:13 kube-system_aws-node-r78x8_3e054baa-fecb-4e2f-a269-73124c95603b
drwxr-xr-x 3 root root 21 Dec 14 03:13 kube-system_coredns-54bc78bc49-662nj_295cc684-7a66-4c4b-ae97-5c728ba6593e
drwxr-xr-x 3 root root 24 Dec 14 03:13 kube-system_kube-proxy-9ccf5_6b606d7f-e139-4b04-81cb-9cf81d39bb62
drwxr-xr-x 5 root root 66 Dec 14 04:00 linkerd_linkerd-destination-56578b6779-g8zbx_906680d6-0c01-4edb-8234-f51639980d1e
drwxr-xr-x 5 root root 69 Dec 14 04:00 linkerd_linkerd-proxy-injector-7674b595d5-bpftr_04183c88-0434-4afa-80d7-028326362101
drwxr-xr-x 5 root root 67 Dec 14 04:00 linkerd_linkerd-sp-validator-5d7bb655ff-7rc45_ba4033e6-2a0f-46de-9196-ed2922b4a0e2
```