Kubelet use cluster-wide root CA, not per-node (bsc#1155810) #832
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jenting
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jenting
requested review from
ereslibre,
Klaven,
innobead,
c3y1huang,
cclhsu,
maximenoel8 and
flavio
Signed-off-by: JenTing Hsiao <[email protected]>
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LGTM, just one more thing to confirm. Do you have any idea for cert rotation? P.S. iirc we also do not take care in the current skuba as well for kubelet cert rotation, because |
This PR also address the server cert rotation via node upgrade.
If we want to make server certificate rotation automatically not by node upgrade, we need to have a PKI server in K8s cluster to signing the CSR request from kubelet, but I did not take this design into skuba since we have an internal CSR signer like this repo and this might have other security issues. |
| host := t.target.Nodename | ||
| altNames := certutil.AltNames{} | ||
| if ip := net.ParseIP(host); ip != nil { | ||
| altNames.IPs = append(altNames.IPs, ip) | ||
| } else { | ||
| altNames.DNSNames = append(altNames.DNSNames, host) | ||
| } | ||
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| // Create AltNames with defaults DNSNames/IPs | ||
| stdout, _, err := t.silentSsh("hostname", "-I") | ||
| if err != nil { | ||
| return err | ||
| } | ||
| for _, addr := range strings.Split(stdout, " ") { | ||
| if ip := net.ParseIP(addr); ip != nil { | ||
| altNames.IPs = append(altNames.IPs, ip) | ||
| } | ||
| } | ||
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| alternateIPs := []net.IP{net.ParseIP(t.target.Target), net.IPv4(127, 0, 0, 1), net.IPv6loopback} | ||
| alternateDNS := []string{"localhost"} |
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I need to better understand the metrics-server, but I'm going to make some assumptions, please correct me if I'm wrong.
- The metrics-server lists the nodes in the cluster using the kube api
- The metrics-server then lists for each node the IP addresses and DNS names [if any] (internal, external...)
As I understand, its --kubelet-preferred-address-types argument determines how it will try to reach each Kubelet API (e.g. InternalIP,ExternalIP,Hostname -- as per https://github.com/kubernetes-sigs/metrics-server/blob/019bda9fb8562dbc7996f0c38e31c709628df316/README.md).
Then, what I wonder what our recommendation will be. Some thoughts:
-
The
InternalIPwill be detected by this script by runninghostname -I(command that doesn't work on all distros btw, but that's a different story). However, the metrics-server might be unable to talk to theInternalIPof the kubelets -- maybe it isn't routable -- -
The
ExternalIPwon't be always available, e.g. if we deployed on top of OpenStack without cloud integration. Also, in case we had this enabled, our certificate would not include this external IP, since the machine doesn't know about this IP address, and is some upper layer using this IP address and routing traffic to the internal IP (the one that we know about), but the certificate wouldn't include the external IP and we wouldn't have any way to autodetect it prior to the kubelet registering. -
About
Hostname, I don't think our certificate would include this in any way, because we cannot know what external hostname the node has without cloud integration.
So I think we want to think about how are we going to do this integration, mostly for the different cases, and also, to what extent we want to play "smart" and autodetect many things, and to what extent we just want to ask the user on the CLI for extra SAN's directly, so they can populate those directly from the CLI, since I fear there are some cases that we will not be able to autodetect.
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I need to better understand the metrics-server, but I'm going to make some assumptions, please correct me if I'm wrong.
- The metrics-server lists the nodes in the cluster using the kube api
- The metrics-server then lists for each node the IP addresses and DNS names [if any] (internal, external...)
As I understand, its
--kubelet-preferred-address-typesargument determines how it will try to reach each Kubelet API (e.g.InternalIP,ExternalIP,Hostname-- as per https://github.com/kubernetes-sigs/metrics-server/blob/019bda9fb8562dbc7996f0c38e31c709628df316/README.md).Then, what I wonder what our recommendation will be. Some thoughts:
- The
InternalIPwill be detected by this script by runninghostname -I(command that doesn't work on all distros btw, but that's a different story). However, the metrics-server might be unable to talk to theInternalIPof the kubelets -- maybe it isn't routable --
In my opinion, the main purpose of metrics-server is to let kubectl top [pod|node] commands work, and further, let Horizontal Pod Autoscaling works.
Therefore, I assume that the user would install metrics-server inside the Kubernetes cluster that the in-cluster networking is routable to each component.
But there have other scenarios like the user use curl command or other tools outside Kubernetes cluster to scrape the kubelet node metrics, I have not thought this too much to be honest.
- The
ExternalIPwon't be always available, e.g. if we deployed on top of OpenStack without cloud integration. Also, in case we had this enabled, our certificate would not include this external IP, since the machine doesn't know about this IP address, and is some upper layer using this IP address and routing traffic to the internal IP (the one that we know about), but the certificate wouldn't include the external IP and we wouldn't have any way to autodetect it prior to the kubelet registering.
ExternalIP is filled as skuba bootstrap/join --target <ip-address/fqdn>.
I had tested on OpenStack, and you are right, metrics-server can only access to kubelet with InternalIP, not ExternalIP.
- About
Hostname, I don't think our certificate would include this in any way, because we cannot know what external hostname the node has without cloud integration.
Now, the hostname is filled the same as skuba bootstrap/join .
Actually, kubelet self-signed server certificate SAN only contains the nodename, and mostly it is not accessible from metrics-server since the hostname cannot be resolved in CoreDNS.
So I think we want to think about how are we going to do this integration, mostly for the different cases, and also, to what extent we want to play "smart" and autodetect many things, and to what extent we just want to ask the user on the CLI for extra SAN's directly, so they can populate those directly from the CLI, since I fear there are some cases that we will not be able to autodetect.
Let the user inputs extra SAN's might not help too much since each node has a different IP address/FQDN.
The smarter way is to sign as many SANs into the server certificate as possible.
I had only double verified this PR on OpenStack, I think we could ask QA for help to double verify on VMWare and bare-metal (KVM might needed in the future).
The one way I am not pretty sure is integrated with the cloud provider. I am not sure which DHCP server assigns each node IP address. If you have any idea, provides it to me, please.
BTW, I take ETCD as a reference for the SAN's field, that's why the SAN have IPv4/IPv6 loopback interface in it.
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In my opinion, the main purpose of metrics-server is to let kubectl top [pod|node] commands work, and further, let Horizontal Pod Autoscaling works.
👍, yes.
Therefore, I assume that the user would install metrics-server inside the Kubernetes cluster that the in-cluster networking is routable to each component.
Absolutely, all my comments were assuming the metrics-server is installed as a regular cluster workload.
Let the user inputs extra SAN's might not help too much since each node has a different IP address/FQDN.
Hm, what I had in mind is to provide the extra SANs on every bootstrap/join command for that specific Kubelet API, keep reading on the next point :)
The smarter way is to sign as many SANs into the server certificate as possible.
Let's keep as it is for now, as simple as possible, and if we see that we are lacking some entries on some environments that we cannot foresee right now.
If we see we are missing some SANs I would be in favour of being more secure, so for each skuba node bootstrap and skuba node join they would be able to provide a --kubelet-api-extra-sans argument to both commands. Ideally, this should be saved inside our skuba-config ConfigMap inside a map or something similar (e.g. with key nodename and value a list of extra sans), so we can keep this configuration when renewing certificates without having to ask for this arguments in the future again.
Also, as an aside, I would have to check, but I wonder how the kubelet behaves if it has cloud integration enabled. Will it recreate the kubelet API certificate if it has cloud integration, when ExternalDNS or ExternalIP is filled by the cloud integration, and will it add those entries to the local kubelet API certificate? In that case our solution wouldn't be explicitly a superset of the certificate generated by the kubelet.
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Just checked, everything should be fine, even with cloud integration enabled. This is the certificate we are generating for the kubelet API with this PR:
caasp-master-ereslibre-0:/var/lib/kubelet/pki # openssl x509 -in kubelet.crt -noout -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 6430524848358850734 (0x593dd04779c080ae)
Signature Algorithm: sha256WithRSAEncryption
Issuer: CN = kubelet-ca
Validity
Not Before: Nov 22 11:36:08 2019 GMT
Not After : Nov 21 11:36:52 2020 GMT
Subject: CN = caasp-master-ereslibre-0
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (2048 bit)
Modulus:
00:b4:0e:fb:51:84:5c:dc:5c:61:05:11:e3:bc:bf:
32:77:c4:8a:57:67:34:9b:17:0d:1e:ce:47:93:35:
de:dd:81:e6:56:07:ef:14:bc:1e:e5:09:2c:84:94:
de:57:39:0e:59:01:c2:37:01:71:f5:8e:45:cf:f3:
35:c4:29:6e:5a:17:2f:99:f7:74:55:6d:49:2c:0c:
e8:5d:54:d9:8e:53:44:fe:c3:02:3f:f7:06:4e:23:
b1:09:a3:04:c4:62:c0:9c:ca:d4:44:bc:d4:1a:48:
85:bd:d6:b7:47:9d:fe:9c:a2:81:a4:b5:5f:a4:4c:
5d:a6:de:d1:32:3f:ee:7a:6c:21:f2:65:e8:6e:7a:
97:97:0d:aa:7c:e5:85:b5:f4:8a:81:95:cd:b3:12:
e7:f8:30:f0:54:ca:04:06:5c:fd:3e:ac:97:3e:17:
32:10:ec:6a:c6:f4:48:6a:db:cf:bc:69:05:b5:52:
22:b2:3b:a1:79:d8:15:33:ea:5a:13:0e:c3:f1:e9:
a8:48:ca:dc:e3:a7:b8:cb:b0:b6:44:69:c5:38:86:
77:08:c2:38:a5:ab:0a:bf:d3:0a:5f:2a:64:a3:c7:
de:71:2e:0b:34:4c:e0:de:d6:c0:b2:70:e2:de:47:
4c:fb:79:a9:27:e1:35:72:53:03:75:a0:86:c8:69:
2a:3b
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Key Encipherment
X509v3 Extended Key Usage:
TLS Web Server Authentication
X509v3 Subject Alternative Name:
DNS:caasp-master-ereslibre-0, DNS:localhost, IP Address:172.28.0.6, IP Address:10.86.0.196, IP Address:127.0.0.1, IP Address:0:0:0:0:0:0:0:1
Signature Algorithm: sha256WithRSAEncryption
7e:c3:2a:e2:bb:fc:48:07:aa:f7:9f:61:c7:75:d8:17:f8:c2:
fc:6d:24:bf:8c:ed:b3:43:97:ee:54:c0:1d:73:1c:7b:0c:9b:
58:3f:83:4e:4d:00:d8:93:22:a2:c8:d2:0b:f3:78:c3:6e:2d:
a1:3e:9e:3b:6f:63:a2:96:2e:55:59:69:f9:f1:f2:36:2b:5e:
68:3d:6b:7c:d3:62:81:b8:95:18:a0:21:b6:4d:00:a0:a1:b2:
37:7b:1a:d3:d7:fb:be:2a:00:37:ec:c9:71:d3:91:0d:ca:f9:
cc:f1:12:c1:96:8b:16:50:03:53:42:35:21:77:9f:43:fa:2c:
f5:8a:75:4f:c6:eb:70:61:c9:53:2b:f8:bf:23:78:3f:fc:60:
b9:a2:76:2b:69:15:71:dd:69:03:cd:c6:f1:c4:d7:00:08:0a:
c9:2e:69:81:07:9e:3a:ed:13:49:f0:93:83:8e:c9:e4:ac:d2:
ac:31:aa:c6:a4:28:36:24:77:ff:9e:15:e1:43:68:9b:4c:2a:
e6:74:65:84:12:ec:21:e4:0b:db:22:ef:83:96:a8:3f:e9:5d:
4b:45:dc:80:69:e0:93:9e:a4:9a:0e:29:4f:a9:bb:1e:1c:67:
8c:89:8b:9a:b9:da:c9:49:6d:ec:71:e5:69:dc:13:b1:7e:f9:
43:a3:9d:de
I tried to remove all files: kubelet-ca.{crt,key} and kubelet.{crt,key}, restart the kubelet, and this was the certificate I got for kubelet.crt:
caasp-master-ereslibre-0:/var/lib/kubelet/pki # openssl x509 -in kubelet.crt -noout -text
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 2 (0x2)
Signature Algorithm: sha256WithRSAEncryption
Issuer: CN = caasp-master-ereslibre-0-ca@1574422971
Validity
Not Before: Nov 22 10:42:50 2019 GMT
Not After : Nov 21 10:42:50 2020 GMT
Subject: CN = caasp-master-ereslibre-0@1574422972
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (2048 bit)
Modulus:
00:c2:03:fb:70:52:d1:4a:53:8e:62:a9:1f:93:09:
00:a6:78:ee:59:e4:15:c4:cb:9c:24:90:59:f3:51:
a3:d5:25:d4:55:69:f0:3d:7d:43:70:f1:14:a5:77:
2a:e5:c5:65:2a:15:3e:7e:1a:8a:28:67:80:83:ad:
be:c4:ae:6a:cb:e4:27:8f:55:d6:90:85:2a:69:09:
d1:c1:72:b6:7b:b2:5e:80:fc:6d:1b:eb:b7:4b:b9:
9f:fb:57:2c:4c:59:35:ca:98:c2:61:f7:45:ad:ef:
6e:a8:dd:b1:fb:ad:eb:8f:ae:57:17:5a:67:25:2a:
d0:43:54:3f:c2:4b:db:e1:74:b5:ff:83:8f:54:dd:
b6:e3:89:2e:69:e7:24:38:8a:63:1a:8d:f4:18:be:
4f:9a:70:98:27:c8:85:8f:3c:5e:65:db:98:8b:fb:
6e:87:02:c0:6b:9b:9c:01:e2:ab:15:cc:e4:59:bc:
20:cd:c3:81:c4:75:28:1c:8e:78:45:f2:b6:32:cf:
92:23:65:37:76:b7:d9:0e:c4:72:9b:44:04:c1:89:
81:e6:c5:9b:b5:8d:b9:42:2d:ce:15:d6:7f:1d:58:
87:6b:3f:49:f7:eb:10:4a:e1:af:b8:f3:a8:b9:32:
21:78:3e:dc:2e:b0:a7:ee:f8:6c:8d:01:c3:fd:41:
a8:4f
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Key Encipherment
X509v3 Extended Key Usage:
TLS Web Server Authentication
X509v3 Basic Constraints: critical
CA:FALSE
X509v3 Subject Alternative Name:
DNS:caasp-master-ereslibre-0
Signature Algorithm: sha256WithRSAEncryption
0a:b7:2d:d3:82:fd:17:7e:44:b7:60:d8:14:79:e9:08:66:a7:
f2:f1:fb:7c:d3:89:37:8a:4b:45:45:17:fb:82:28:06:d0:58:
91:75:dd:5e:5e:b3:c1:8f:83:b2:e5:e1:7a:12:e1:31:15:a5:
c1:22:b9:7f:86:f7:65:cd:da:56:2e:d3:0d:25:e7:86:d9:e1:
a8:5f:ec:55:ac:cd:26:02:1c:3f:93:16:89:18:76:d9:bb:73:
a0:c1:77:f9:ba:19:9a:b7:c0:b0:75:a3:60:5f:70:05:4c:58:
76:02:6d:f5:a3:93:48:98:84:51:6f:78:f3:3f:4b:a9:a0:bc:
3d:15:6e:35:8d:3f:a4:4f:3b:fe:c4:fc:fa:b7:35:20:57:b8:
1f:02:19:f6:e7:0c:3f:22:59:cd:e7:a9:90:d6:82:bc:41:2c:
c9:9d:b6:2a:9e:b0:6f:14:48:92:c6:b8:8e:03:f6:77:52:98:
39:a7:f4:fd:d5:15:93:ee:76:a8:ed:e5:0d:9d:e3:d6:2d:3b:
a9:c3:00:d1:e7:12:51:81:9e:d2:65:d7:a8:5e:83:a1:c8:48:
47:2d:90:4a:01:d0:41:4a:d4:d6:89:57:69:16:e0:37:7f:8c:
b8:bd:09:b6:22:fc:82:0b:56:ed:24:ae:d0:56:7e:b1:c1:13:
47:e1:d0:fb
So everything should be fine. Thank you @jenting for all the information.
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Just come out a thought, correct me if I am wrong. Would it better? |
Hm, I'm not sure. Because we would have to let the kubelet register first, then read the node using the Kubernetes API, create our certificate, upload certificate overriding the one created by the kubelet and restart the kubelet service. I think the current approach is better in terms of simplicity and we can evolve with more knowledge from the field and stakeholders. The only thing I'm concerned about is how the kubelet behaves with cloud integration, whether it also adds to the kubelet API SANs the ExternalDNS and ExternalIP to the kubelet API certificate or not. Because this would be something that we just cannot anticipate prior to bootstrapping/joining the node. |
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More questions (sorry, I'm starting to dig into this):
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I had tested this feature before, it does not work since we do not have a custom CSR signer in current Kubernetes cluster. Therefore, when enable this feature, by default kubelet generates a CSR request, but kube-controller won’t sign the CSR to kubelet. Unless we provides a CSR signer in the cluster. Please reference to this comment #832 (comment)
Two reasons:
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QA information :Building skuba :
Testing environment :
Cluster setting :I'm using the new option --kubernetes-version to be able to upgrade once the cluster is deployed Scenario:I want to deploy metrics on my cluster WITHOUT the insecure mode and get access to kubectl top nodes and kubectl top pods -n kube-system Before :
Result: and
Test:
Result:
Result: CommentsThe test is PASS on Vmware. I was able to access the metrics from metrics server. And the certificate are correctly deploy on all the nodes. |
Why is this PR needed?
Kubelet self-signed root CA per-node and also self-signed kubelet server certificate, this cause external service like metrics-server cannot use trusted TLS to get CPU/memory information from kubelet.
Now, all the recommended way to integrate metric-server is to add
kubelet-insecure-tlsflag, which is not suitable for a production-grade cluster.Fixes https://github.com/SUSE/avant-garde/issues/1005
Reminder: Add the "fixes bsc#XXXX" to the title of the commit so that it will
appear in the changelog.
What does this PR do?
kubelet-caand store thekubelet-ca.crt/kubelet-ca.keyto local bootstrap folder.kubelet-ca.crt/kubelet-ca.keyto all the control plane node/var/lib/kubelet/pki/kubelet-ca.crt//var/lib/kubelet/pki/kubelet-ca.keykubelet-ca.crtto all the worker node/var/lib/kubelet/pki/kubelet-ca.crtkubelet.crt/kubelet.keyto/var/lib/kubelet/pki/kubelet.crt//var/lib/kubelet/pki/kubelet.keyAnything else a reviewer needs to know?
This PR includes the following scenarios:
Info for QA
Please follow the steps on Status BEFORE/AFTER applying the patch on how to validate this.
Please double verify on all the platforms: OpenStack, VMWare, Bare Metal.
Related info
Info that can be relevant for QA:
Status BEFORE applying the patch
The only way to install metrics-server is to use insecure-TLS mode.
metrics-server could fetch CPU/Memory from kubelet node port 10250 without TLS, so
kubectl top node/kubectl top podhave information out.Status AFTER applying the patch
Mount the kubelet root CA certificate from host path and tell the metrics-server where path of kubelet-certificate-authority is.
metrics-server could fetch CPU/Memory from kubelet node port 10250 with TLS, so
kubectl top node/kubectl top podhave information out.Docs
SUSE/doc-caasp#602
Merge restrictions
(Please do not edit this)
We are in v4-maintenance phase, so we will restrict what can be merged to prevent unexpected surprises:
Signed-off-by: JenTing Hsiao [email protected]