* Build Kubelet container images internally and publish
to Quay and Dockerhub (new) as an alternative in case of
registry outage or breach
* Use our infra to provide single and multi-arch (default)
Kublet images for possible future use
* Docs: Show how to use alternative Kubelet images via
snippets and a systemd dropin (builds on #737)
Changes:
* Update docs with changes to Kubelet image building
* If you prefer to trust images built by Quay/Dockerhub,
automated image builds are still available with unique
tags (albeit with some limitations):
* Quay automated builds are tagged `build-{short_sha}`
(limit: only amd64)
* Dockerhub automated builts are tagged `build-{tag}`
and `build-master` (limit: only amd64, no shas)
Links:
* Kubelet: https://github.com/poseidon/kubelet
* Docs: https://typhoon.psdn.io/topics/security/#container-images
* Registries:
* quay.io/poseidon/kubelet
* docker.io/psdn/kubelet
* Promote DigitalOcean from alpha to beta for Fedora
CoreOS and Flatcar Linux
* Upgrade mkdocs-material and PyPI packages for docs
* Replace docs mentions of Container Linux with Flatcar
Linux and move docs/cl to docs/flatcar-linux
* Deprecate CoreOS Container Linux support. Its still
usable for some time, but start removing docs
* Set a consistent MCS level/range for Calico install-cni
* Note: Rebooting a node was a workaround, because Kubelet
relabels /etc/kubernetes(/cni/net.d)
Background:
* On SELinux enforcing systems, the Calico CNI install-cni
container ran with default SELinux context and a random MCS
pair. install-cni places CNI configs by first creating a
temporary file and then moving them into place, which means
the file MCS categories depend on the containers SELinux
context.
* calico-node Pod restarts creates a new install-cni container
with a different MCS pair that cannot access the earlier
written file (it places configs every time), causing the
init container to error and calico-node to crash loop
* https://github.com/projectcalico/cni-plugin/issues/874
```
mv: inter-device move failed: '/calico.conf.tmp' to
'/host/etc/cni/net.d/10-calico.conflist'; unable to remove target:
Permission denied
Failed to mv files. This may be caused by selinux configuration on
the
host, or something else.
```
Note, this isn't a host SELinux configuration issue.
Related:
* https://github.com/poseidon/terraform-render-bootstrap/pull/186
* Enable bootstrap token authentication on kube-apiserver
* Generate the bootstrap.kubernetes.io/token Secret that
may be used as a bootstrap token
* Generate a bootstrap kubeconfig (with a bootstrap token)
to be securely distributed to nodes. Each Kubelet will use
the bootstrap kubeconfig to authenticate to kube-apiserver
as `system:bootstrappers` and send a node-unique CSR for
kube-controller-manager to automatically approve to issue
a Kubelet certificate and kubeconfig (expires in 72 hours)
* Add ClusterRoleBinding for bootstrap token subjects
(`system:bootstrappers`) to have the `system:node-bootstrapper`
ClusterRole
* Add ClusterRoleBinding for bootstrap token subjects
(`system:bootstrappers`) to have the csr nodeclient ClusterRole
* Add ClusterRoleBinding for bootstrap token subjects
(`system:bootstrappers`) to have the csr selfnodeclient ClusterRole
* Enable NodeRestriction admission controller to limit the
scope of Node or Pod objects a Kubelet can modify to those of
the node itself
* Ability for a Kubelet to delete its Node object is retained
as preemptible nodes or those in auto-scaling instance groups
need to be able to remove themselves on shutdown. This need
continues to have precedence over any risk of a node deleting
itself maliciously
Security notes:
1. Issued Kubelet certificates authenticate as user `system:node:NAME`
and group `system:nodes` and are limited in their authorization
to perform API operations by Node authorization and NodeRestriction
admission. Previously, a Kubelet's authorization was broader. This
is the primary security motivation.
2. The bootstrap kubeconfig credential has the same sensitivity
as the previous generated TLS client-certificate kubeconfig.
It must be distributed securely to nodes. Its compromise still
allows an attacker to obtain a Kubelet kubeconfig
3. Bootstrapping Kubelet kubeconfig's with a limited lifetime offers
a slight security improvement.
* An attacker who obtains the kubeconfig can likely obtain the
bootstrap kubeconfig as well, to obtain the ability to renew
their access
* A compromised bootstrap kubeconfig could plausibly be handled
by replacing the bootstrap token Secret, distributing the token
to new nodes, and expiration. Whereas a compromised TLS-client
certificate kubeconfig can't be revoked (no CRL). However,
replacing a bootstrap token can be impractical in real cluster
environments, so the limited lifetime is mostly a theoretical
benefit.
* Cluster CSR objects are visible via kubectl which is nice
4. Bootstrapping node-unique Kubelet kubeconfigs means Kubelet
clients have more identity information, which can improve the
utility of audits and future features
Rel: https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/
Rel: https://github.com/poseidon/terraform-render-bootstrap/pull/185
* DigitalOcean firewall rules should reference Terraform tag
resources rather than using tag strings. Otherwise, terraform
apply can fail (neeeds rerun) if a tag has not yet been created
* Race: During initial bootstrap, static control plane pods
could hang with Permission denied to bootstrap secrets. A
manual fix involved restarting Kubelet, which relabeled mounts
The race had no effect on subsequent reboots.
* bootstrap.service runs podman with a private unshared mount
of /etc/kubernetes/bootstrap-secrets which uses an SELinux MCS
label with a category pair. However, bootstrap-secrets should
be shared as its mounted by Docker pods kube-apiserver,
kube-scheduler, and kube-controller-manager. Restarting Kubelet
was a manual fix because Kubelet relabels all /etc/kubernetes
* Fix bootstrap Pod to use the shared volume label, which leaves
bootstrap-secrets files with SELinux level s0 without MCS
* Also allow failed bootstrap.service to be re-applied. This was
missing on bare-metal and AWS
* Initial support for Flatcar Linux on Azure used the Flatcar
Linux Azure Marketplace images (e.g. `flatcar-stable`) in
https://github.com/poseidon/typhoon/pull/664
* Flatcar Linux Azure Marketplace images have some unresolved
items https://github.com/poseidon/typhoon/issues/703
* Until the Marketplace items are resolved, revert to requiring
Flatcar Linux's images be manually uploaded (like GCP and
DigitalOcean)
* No change to Fedora CoreOS modules
* For Container Linx AWS and Azure, change the `os_image` default
from coreos-stable to flatcar-stable
* For Container Linux GCP and DigitalOcean, change `os_image` to
be required since users should upload a Flatcar Linux image and
set the variable
* For Container Linux bare-metal, recommend users change the
`os_channel` to Flatcar Linux. No actual module change.
* Add "lb" outbound rule for worker TCP _and_ UDP traffic
* Fix Azure worker nodes clock synchronization being inactive
due to timeouts reaching the CoreOS / Flatcar NTP pool
* Fix Azure worker nodes not providing outbount UDP connectivity
Background:
Azure provides VMs outbound connectivity either by having a public
IP or via an SNAT masquerade feature bundled with their virtual
load balancing abstraction (in contrast with, say, a NAT gateway).
Azure worker nodes have only a private IP, but are associated with
the cluster load balancer's backend pool and ingress frontend IP.
Outbound traffic uses SNAT with this frontend IP. A subtle detail
with Azure SNAT seems to be that since both inbound lb_rule's are
TCP only, outbound UDP traffic isn't SNAT'd (highlights the reasons
Azure shouldn't have conflated inbound load balancing with outbound
SNAT concepts). However, adding a separate outbound rule and
disabling outbound SNAT on our ingress lb_rule's we can tell Azure
to continue load balancing as before, and support outbound SNAT for
worker traffic of both the TCP and UDP protocol.
Fixes clock synchronization timeouts:
```
systemd-timesyncd[786]: Timed out waiting for reply from
45.79.36.123:123 (3.flatcar.pool.ntp.org)
```
Azure controller nodes have their own public IP, so controllers (and
etcd) nodes have not had clock synchronization or outbound UDP issues
* Fix bootstrap error for missing `manifests-networking/crd*yaml`
when `networking = "flannel"`
* Cleanup manifest-networking directory left during bootstrap
* Regressed in v1.18.0 changes for Calico https://github.com/poseidon/typhoon/pull/675
* Change kube-proxy, flannel, and calico-node DaemonSet
tolerations to tolerate `node.kubernetes.io/not-ready`
and `node-role.kubernetes.io/master` (i.e. controllers)
explicitly, rather than tolerating all taints
* kube-system DaemonSets will no longer tolerate custom
node taints by default. Instead, custom node taints must
be enumerated to opt-in to scheduling/executing the
kube-system DaemonSets
* Consider setting the daemonset_tolerations variable
of terraform-render-bootstrap at a later date
Background: Tolerating all taints ruled out use-cases
where certain nodes might legitimately need to keep
kube-proxy or CNI networking disabled
Related: https://github.com/poseidon/terraform-render-bootstrap/pull/179
* Problem: Fedora CoreOS images are manually uploaded to GCP. When a
cluster is created with a stale image, Zincati immediately checks
for the latest stable image, fetches, and reboots. In practice,
this can unfortunately occur exactly during the initial cluster
bootstrap phase.
* Recommended: Upload the latest Fedora CoreOS image regularly
* Mitigation: Allow a failed bootstrap.service run (which won't touch
the done ConditionalPathExists) to be re-run by running `terraforma apply`
again. Add a known issue to CHANGES
* Update docs to show the current Fedora CoreOS stable version to
reduce likelihood users see this issue
Longer term ideas:
* Ideal: Fedora CoreOS publishes a stable channel. Instances will always
boot with the latest image in a channel. The problem disappears since
it works the same way AWS does
* Timer: Consider some timer-based approach to have zincati delay any
system reboots for the first ~30 min of a machine's life. Possibly just
configured on the controller node https://github.com/coreos/zincati/pull/251
* External coordination: For Container Linux, locksmith filled a similar
role and was disabled to allow CLUO to coordinate reboots. By running
atop Kubernetes, it was not possible for the reboot to occur before
cluster bootstrap
* Rely on https://github.com/coreos/zincati/issues/115 to delay the
reboot since bootstrap involves an SSH session
* Use path-based activation of zincati on controllers and set that
path at the end of the bootstrap process
Rel: https://github.com/coreos/fedora-coreos-tracker/issues/239
* Fix issue observed in us-east-1 where AMI filters chose the
latest testing channel release, rather than the stable chanel
* Fedora CoreOS AMI filter selects the latest image with a
matching name, x86_64, and hvm, excluding dev images. Add a
filter for "Fedora CoreOS stable", which seems to be the only
distinguishing metadata indicating the channel
* Recommend that users who have not yet tried Fedora CoreOS or
Flatcar Linux do so. Likely, Container Linux will reach EOL
and platform support / stability ratings will be in a mixed
state. Nevertheless, folks should migrate by September.
* Before Kubernetes v1.18.0, Kubelet only supported kubectl
`--limit-bytes` with the Docker `json-file` log driver so
the Fedora CoreOS default was overridden for conformance.
See https://github.com/poseidon/typhoon/pull/642
* Kubelet v1.18+ implemented support for other docker log
drivers, so the Fedora CoreOS default `journald` can be
used again
Rel: https://github.com/kubernetes/kubernetes/issues/86367
Dalton Hubble