* Write the systemd kubelet.service to use `KUBELET_IMAGE`
as the Kubelet. This provides a nice way to use systemd
dropins to temporarily override the image (e.g. during a
registry outage)
Note: Only Typhoon Kubelet images and registries are supported.
* 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
* 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
* In v1.18.0, kubectl apply would fail to apply manifests if any
single manifest was unable to validate. For example, if a CRD and
CR were defined in the same directory, apply would fail since the
CR would be invalid as the CRD wouldn't exist
* Typhoon temporary workaround was to separate CNI CRD manifests
and explicitly apply them first. No longer needed in v1.18.1+
* Kubernetes v1.18.1 restored the prior behavior where kubectl apply
applies as many valid manifests as it can. In the example above, the
CRD would be applied and the CR could be applied if the kubectl apply
was re-run (allowing for apply loops).
* Upstream fix: https://github.com/kubernetes/kubernetes/pull/89864
* 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.
* 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
* 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
* Fix delete-node service that runs on worker (cloud-only)
shutdown to delete a Kubernetes node. Regressed in #669
(unreleased)
* Use rkt `--exec` to invoke kubectl binary in the kubelet
image
* Use podman `--entrypoint` to invoke the kubectl binary in
the kubelet image
* 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
* Kubernetes plans to stop releasing the hyperkube container image
* Upstream will continue to publish `kube-apiserver`, `kube-controller-manager`,
`kube-scheduler`, and `kube-proxy` container images to `k8s.gcr.io`
* Upstream will publish Kubelet only as a binary for distros to package,
either as a DEB/RPM on traditional distros or a container image on
container-optimized operating systems
* Typhoon will package the upstream Kubelet (checksummed) and its
dependencies as a container image for use on CoreOS Container Linux,
Flatcar Linux, and Fedora CoreOS
* Update the Typhoon container image security policy to list
`quay.io/poseidon/kubelet`as an official distributed artifact
Hyperkube: https://github.com/kubernetes/kubernetes/pull/88676
Kubelet Container Image: https://github.com/poseidon/kubelet
Kubelet Quay Repo: https://quay.io/repository/poseidon/kubelet
* Quay has historically generated ACI signatures for images to
facilitate rkt's notions of verification (it allowed authors to
actually sign images, though `--trust-keys-from-https` is in use
since etcd and most authors don't sign images). OCI standardization
didn't adopt verification ideas and checking signatures has fallen
out of favor.
* Fix an issue where Quay no longer seems to be generating ACI
signatures for new images (e.g. quay.io/coreos/etcd:v.3.4.4)
* Don't be alarmed by rkt `--insecure-options=image`. It refers
to disabling image signature checking (i.e. docker pull doesn't
check signatures either)
* System containers for Kubelet and bootstrap have transitioned
to the docker:// transport, so there is precedent and this brings
all the system containers on Container Linux controllers into
alignment
* On clouds where workers can scale down or be preempted
(AWS, GCP, Azure), shutdown runs delete-node.service to
remove a node a prevent NotReady nodes from lingering
* Add the delete-node.service that wasn't carried over
from Container Linux and port it to use podman
* Allow users to extend the route table using a data reference
and adding route resources (e.g. unusual peering setups)
* Note: Internally connecting AWS clusters can reduce cross-cloud
flexibility and inhibits blue-green cluster patterns. It is not
recommended
* Add Terraform strip markers to consume beginning and
trailing whitespace in templated Kubelet arguments for
podman (Fedora CoreOS only)
* Fix initial `worker_node_labels` being quietly ignored
on Fedora CoreOS cloud platforms that offer the feature
* Close https://github.com/poseidon/typhoon/issues/650
* Fix the last minor issue for Fedora CoreOS clusters to pass CNCF's
Kubernetes conformance tests
* Kubelet supports a seldom used feature `kubectl logs --limit-bytes=N`
to trim a log stream to a desired length. Kubelet handles this in the
CRI driver. The Kubelet docker shim only supports the limit bytes
feature when Docker is configured with the default `json-file` logging
driver
* CNCF conformance tests started requiring limit-bytes be supported,
indirectly forcing the log driver choice until either the Kubelet or
the conformance tests are fixed
* Fedora CoreOS defaults Docker to use `journald` (desired). For now,
as a workaround to offer conformant clusters, the log driver can
be set back to `json-file`. RHEL CoreOS likely won't have noticed the
non-conformance since its using crio runtime
* https://github.com/kubernetes/kubernetes/issues/86367
Note: When upstream has a fix, the aim is to drop the docker config
override and use the journald default
* Select the most recent fedora-coreos-31 AMI on AWS, instead
of the most recent fedora-coreos-30 AMI (Nov 27, 2019)
* Evaluated with fedora-coreos-31.20200108.2.0-hvm
* Configure kube-proxy --metrics-bind-address=0.0.0.0 (default
127.0.0.1) to serve metrics on 0.0.0.0:10249
* Add firewall rules to allow Prometheus (resides on a worker) to
scrape kube-proxy service endpoints on controllers or workers
* Add a clusterIP: None service for kube-proxy endpoint discovery
* Change kubelet.service on Container Linux nodes to ExecStart Kubelet
inline to replace the use of the host OS kubelet-wrapper script
* Express rkt run flags and volume mounts in a clear, uniform way to
make the Kubelet service easier to audit, manage, and understand
* Eliminate reliance on a Container Linux kubelet-wrapper script
* Typhoon for Fedora CoreOS developed a kubelet.service that similarly
uses an inline ExecStart (except with podman instead of rkt) and a
more minimal set of volume mounts. Adopt the volume improvements:
* Change Kubelet /etc/kubernetes volume to read-only
* Change Kubelet /etc/resolv.conf volume to read-only
* Remove unneeded /var/lib/cni volume mount
Background:
* kubelet-wrapper was added in CoreOS around the time of Kubernetes v1.0
to simplify running a CoreOS-built hyperkube ACI image via rkt-fly. The
script defaults are no longer ideal (e.g. rkt's notion of trust dates
back to quay.io ACI image serving and signing, which informed the OCI
standard images we use today, though they still lack rkt's signing ideas).
* Shipping kubelet-wrapper was regretted at CoreOS, but remains in the
distro for compatibility. The script is not updated to track hyperkube
changes, but it is stable and kubelet.env overrides bridge most gaps
* Typhoon Container Linux nodes have used kubelet-wrapper to rkt/rkt-fly
run the Kubelet via the official k8s.gcr.io hyperkube image using overrides
(new image registry, new image format, restart handling, new mounts, new
entrypoint in v1.17).
* Observation: Most of what it takes to run a Kubelet container is defined
in Typhoon, not in kubelet-wrapper. The wrapper's value is now undermined
by having to workaround its dated defaults. Typhoon may be better served
defining Kubelet.service explicitly
* Typhoon for Fedora CoreOS developed a kubelet.service without the use
of a host OS kubelet-wrapper which is both clearer and eliminated some
volume mounts
* Rename Container Linux Config (CLC) files to *.yaml to align
with Fedora CoreOS Config (FCC) files and for syntax highlighting
* Replace common uses of Terraform `element` (which wraps around)
with `list[index]` syntax to surface index errors
* Original tutorials favored including the platform (e.g.
google-cloud) in modules (e.g. google-cloud-yavin). Prefer
naming conventions where each module / cluster has a simple
name (e.g. yavin) since the platform is usually redundant
* Retain the example cluster naming themes per platform
* Allow generated assets (TLS materials, manifests) to be
securely distributed to controller node(s) via file provisioner
(i.e. ssh-agent) as an assets bundle file, rather than relying
on assets being locally rendered to disk in an asset_dir and
then securely distributed
* Change `asset_dir` from required to optional. Left unset,
asset_dir defaults to "" and no assets will be written to
files on the machine that runs terraform apply
* Enhancement: Managed cluster assets are kept only in Terraform
state, which supports different backends (GCS, S3, etcd, etc) and
optional encryption. terraform apply accesses state, runs in-memory,
and distributes sensitive materials to controllers without making
use of local disk (simplifies use in CI systems)
* Enhancement: Improve asset unpack and layout process to position
etcd certificates and control plane certificates more cleanly,
without unneeded secret materials
Details:
* Terraform file provisioner support for distributing directories of
contents (with unknown structure) has been limited to reading from a
local directory, meaning local writes to asset_dir were required.
https://github.com/poseidon/typhoon/issues/585 discusses the problem
and newer or upcoming Terraform features that might help.
* Observation: Terraform provisioner support for single files works
well, but iteration isn't viable. We're also constrained to Terraform
language features on the apply side (no extra plugins, no shelling out)
and CoreOS / Fedora tools on the receive side.
* Take a map representation of the contents that would have been splayed
out in asset_dir and pack/encode them into a single file format devised
for easy unpacking. Use an awk one-liner on the receive side to unpack.
In pratice, this has worked well and its rather nice that a single
assets file is transferred by file provisioner (all or none)
Rel: https://github.com/poseidon/terraform-render-bootstrap/pull/162
* Set small CPU requests on static pods kube-apiserver,
kube-controller-manager, and kube-scheduler to align with
upstream tooling and for edge cases
* Effectively, a practical case for these requests hasn't been
observed. However, a small static pod CPU request may offer
a slight benefit if a controller became overloaded and the
below mechanisms were insufficient
Existing safeguards:
* Control plane nodes are tainted to isolate them from
ordinary workloads. Even dense workloads can only compress
CPU resources on worker nodes.
* Control plane static pods use the highest priority class, so
contention favors control plane pods (over say node-exporter)
and CPU is compressible too.
See: https://github.com/poseidon/terraform-render-bootstrap/pull/161
* Update terraform-render-bootstrap module to adopt the
Terrform v0.12 templatefile function feature to replace
the use of terraform-provider-template's `template_dir`
* Require Terraform v0.12.6+ which adds `for_each`
Background:
* `template_dir` was added to `terraform-provider-template`
to add support for template directory rendering in CoreOS
Tectonic Kubernetes distribution (~2017)
* Terraform v0.12 introduced a native `templatefile` function
and v0.12.6 introduced native `for_each` support (July 2019)
that makes it possible to replace `template_dir` usage
* Detect the most recent Fedora CoreOS AMI to allow usage
of Fedora CoreOS in supported regions (previously just
us-east-1)
* Unpin the Fedora CoreOS AMI image which was pinned to
images that had been checked. This does mean if Fedora
publishes a broken image, it will be selected
* Filter out "dev" images which have similar naming
* Review variables available in AWS kubernetes and workers
modules and documentation
* Switching between spot and on-demand has worked since
Terraform v0.12
* Generally, there are too many knobs. Less useful ones
should be de-emphasized or removed
* Remove `cluster_domain_suffix` documentation
* Document worker pools `node_labels` variable to set the
initial node labels for a homogeneous set of workers
* Document `worker_node_labels` convenience variable to
set the initial node labels for default worker nodes
* Fix issue (present since bootkube->bootstrap switch) where
controller asset copy could fail if /etc/kubernetes/manifests
wasn't created in time on platforms using path activation for
the Kubelet (observed on DigitalOcean, also possible on
bare-metal)
* Drop `node-role.kubernetes.io/master` and
`node-role.kubernetes.io/node` node labels
* Kubelet (v1.16) now rejects the node labels used
in the kubectl get nodes ROLES output
* https://github.com/kubernetes/kubernetes/issues/75457
* Rename render module from bootkube to bootstrap. Avoid
confusion with the kubernetes-incubator/bootkube tool since
it is no longer used
* Use the poseidon/terraform-render-bootstrap Terraform module
(formerly poseidon/terraform-render-bootkube)
* https://github.com/poseidon/terraform-render-bootkube/pull/149
* Run a kube-apiserver, kube-scheduler, and kube-controller-manager
static pod on each controller node. Previously, kube-apiserver was
self-hosted as a DaemonSet across controllers and kube-scheduler
and kube-controller-manager were a Deployment (with 2 or
controller_count many replicas).
* Remove bootkube bootstrap and pivot to self-hosted
* Remove pod-checkpointer manifests (no longer needed)
* Run a kube-apiserver, kube-scheduler, and kube-controller-manager
static pod on each controller node. Previously, kube-apiserver was
self-hosted as a DaemonSet across controllers and kube-scheduler
and kube-controller-manager were a Deployment (with 2 or
controller_count many replicas).
* Remove bootkube bootstrap and pivot to self-hosted
* Remove pod-checkpointer manifests (no longer needed)
* Run a kube-apiserver, kube-scheduler, and kube-controller-manager
static pod on each controller node. Previously, kube-apiserver was
self-hosted as a DaemonSet across controllers and kube-scheduler
and kube-controller-manager were a Deployment (with 2 or
controller_count many replicas).
* Remove bootkube bootstrap and pivot to self-hosted
* Remove pod-checkpointer manifests (no longer needed)
