kubernetes - 在 Pod 中设置 net.ipv4.tcp_timestamps=0

Question

我想在我的 k8s 集群的 Pod 中设置 net.ipv4.tcp_timestamps=0，但是它给我错误:

sysctl: cannot stat /proc/sys/net/ipv4/tcp_timestamps: No such file or directory"

使用 docker run 命令直接创建的容器存在同样的问题。无论如何要在容器/Pod 中设置参数？谢谢。

Answer 1

在 Kubernetes 中，sysctl 被分为 safe 和 unsafe。

In addition to proper namespacing, a safe sysctl must be properly isolated between pods on the same node. This means that setting a safe sysctl for one pod

• must not have any influence on any other pod on the node
• must not allow to harm the node’s health
• must not allow to gain CPU or memory resources outside of the resource limits of a pod.

By far, most of the namespaced sysctls are not necessarily considered safe. The following sysctls are supported in the safe set:

• kernel.shm_rmid_forced,
• net.ipv4.ip_local_port_range,
• net.ipv4.tcp_syncookies.

默认情况下，所有safe sysctls 都是默认启用的。所有不安全的 sysctl 都被禁用，需要由每个节点上的集群管理员手动允许。

kubelet --allowed-unsafe-sysctls \
 'kernel.msg*,net.core.somaxconn' ...

For Minikube, this can be done via the extra-config flag:

minikube start --extra-config="kubelet.allowed-unsafe-sysctls=kernel.msg*,net.core.somaxconn"...

Only namespaced sysctls can be enabled this way.

这是在 Enabling Unsafe Sysctls 上提到的k8s 文档。

至于，Setting Sysctls for a Pod :

A number of sysctls are namespaced in today’s Linux kernels. This means that they can be set independently for each pod on a node. Only namespaced sysctls are configurable via the pod securityContext within Kubernetes.

The following sysctls are known to be namespaced. This list could change in future versions of the Linux kernel. - kernel.shm*, - kernel.msg*, - kernel.sem, - fs.mqueue.*, - The parameters under net.* that can be set in container networking namespace. However, there are exceptions (e.g., net.netfilter.nf_conntrack_max and net.netfilter.nf_conntrack_expect_max can be set in container networking namespace but they are unnamespaced).

Sysctls with no namespace are called node-level sysctls. If you need to set them, you must manually configure them on each node’s operating system, or by using a DaemonSet with privileged containers.

Use the pod securityContext to configure namespaced sysctls. The securityContext applies to all containers in the same pod.

This example uses the pod securityContext to set a safe sysctl kernel.shm_rmid_forced and two unsafe sysctls net.core.somaxconn and kernel.msgmax. There is no distinction between safe and unsafe sysctls in the specification.

apiVersion: v1
kind: Pod
metadata:
  name: sysctl-example
spec:
  securityContext:
    sysctls:
    - name: kernel.shm_rmid_forced
      value: "0"
    - name: net.core.somaxconn
      value: "1024"
    - name: kernel.msgmax
      value: "65536"
  ...

您可能有兴趣阅读 StackOverflow 上的以下问题 Pros and cons of disabling TCP timestamps和 What benefit is conferred by TCP timestamp? .