Code change:
<ins> --- title: Sidecar Containers content_type: concept weight: 50 --- <!-- overview --> {{< feature-state for_k8s_version="v1.28" state="alpha" >}} Sidecar containers are the secondary containers that run along with the main application container within the same {{< glossary_tooltip text="Pod" term_id="pod" >}}. These containers are used to enhance or to extend the functionality of the main application container by providing additional services, or functionality such as logging, monitoring, security, or data synchronization, without directly altering the primary application code. <!-- body --> ## Enabling sidecar containers Starting with Kubernetes 1.28, a [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) named `SidecarContainers` allows you to specify a `restartPolicy` for containers listed in a Pod's `initContainers` field. These restartable _sidecar_ containers are independent with other [init containers](/docs/concepts/workloads/pods/init-containers/) and main application container within the same pod. These can be started, stopped, or restarted without effecting the main application container and other init containers. ## Sidecar containers and Pod lifecycle If an init container is created with its `restartPolicy` set to `Always`, it will start and remain running during the entire life of the Pod. This can be helpful for running supporting services separated from the main application containers. If a `readinessProbe` is specified for this init container, its result will be used to determine the `ready` state of the Pod. Since these containers are defined as init containers, they benefit from the same ordering and sequential guarantees as other init containers, allowing them to be mixed with other init containers into complex Pod initialization flows. Compared to regular init containers, sidecars defined within `initContainers` continue to run after they have started. This is important when there is more than one entry inside `.spec.initContainers` for a Pod. After a sidecar-style init container is running (the kubelet has set the `started` status for that init container to true), the kubelet then starts the next init container from the ordered `.spec.initContainers` list. That status either becomes true because there is a process running in the container and no startup probe defined, or as a result of its `startupProbe` succeeding. Here's an example of a Deployment with two containers, one of which is a sidecar: {{% code_sample language="yaml" file="application/deployment-sidecar.yaml" %}} This feature is also useful for running Jobs with sidecars, as the sidecar container will not prevent the Job from completing after the main container has finished. Here's an example of a Job with two containers, one of which is a sidecar: {{% code_sample language="yaml" file="application/job/job-sidecar.yaml" %}} By default, this feature is not available in Kubernetes. To avail this feature, you need to enable the [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) named `SidecarContainers`. ## Differences from regular containers Sidecar containers run alongside regular containers in the same pod. However, they do not execute the primary application logic; instead, they provide supporting functionality to the main application. Sidecar containers have their own independent lifecycles. They can be started, stopped, and restarted independently of regular containers. This means you can update, scale, or maintain sidecar containers without affecting the primary application. Sidecar containers share the same network and storage namespaces with the primary container This co-location allows them to interact closely and share resources. ## Differences from init containers Sidecar containers work alongside the main container, extending its functionality and providing additional services. Sidecar containers run concurrently with the main application container. They are active throughout the lifecycle of the pod and can be started and stopped independently of the main container. Unlike [init containers](/docs/concepts/workloads/pods/init-containers/), sidecar containers support [probes](/docs/concepts/workloads/pods/pod-lifecycle/#types-of-probe) to control their lifecycle. These containers can interact directly with the main application containers, sharing the same network namespace, filesystem, and environment variables. They work closely together to provide additional functionality. ## Resource sharing within containers {{< comment >}} This section is also present in the [init containers](/docs/concepts/workloads/pods/init-containers/) page. If you're editing this section, change both places. {{< /comment >}} Given the order of execution for init, sidecar and app containers, the following rules for resource usage apply: * The highest of any particular resource request or limit defined on all init containers is the *effective init request/limit*. If any resource has no resource limit specified this is considered as the highest limit. * The Pod's *effective request/limit* for a resource is the sum of [pod overhead](/docs/concepts/scheduling-eviction/pod-overhead/) and the higher of: * the sum of all non-init containers(app and sidecar containers) request/limit for a resource * the effective init request/limit for a resource * Scheduling is done based on effective requests/limits, which means init containers can reserve resources for initialization that are not used during the life of the Pod. * The QoS (quality of service) tier of the Pod's *effective QoS tier* is the QoS tier for all init, sidecar and app containers alike. Quota and limits are applied based on the effective Pod request and limit. Pod level control groups (cgroups) are based on the effective Pod request and limit, the same as the scheduler. ## {{% heading "whatsnext" %}} * Read a blog post on [native sidecar containers](/blog/2023/08/25/native-sidecar-containers/). * Read about [creating a Pod that has an init container](/docs/tasks/configure-pod-container/configure-pod-initialization/#create-a-pod-that-has-an-init-container). * Learn about the [types of probes](/docs/concepts/workloads/pods/pod-lifecycle/#types-of-probe): liveness, readiness, startup probe. * Learn about [pod overhead](/docs/concepts/scheduling-eviction/pod-overhead/). </ins>

Related discussion:
text: restartPolicy under initContainers is not allowing to create Jobs specified into the below documents Error Message: Job in version "v1" cannot be handled as a Job: strict decoding error: unknown field "[0].restartPolicy" Document Link:
Hi I believe the error message you are getting is because you might have used feild under the section. But it is not allowed under the . /language en
Page related to the issue: /sig docs /sig node
Hi , Below is the Job configuration:
Could you please provide the code block with proper indentation?
updated above section
The indentation should be corrected as below
/kind bug
mentions a feature gate, but doesn't make it explicitly clear that you need to enable it. The feature gate is named . The fix I recommend: add a brand new page edit to direct readers to that new page /remove-kind bug I don't think there is anything actually incorrect. /triage accepted /retitle Unclear documentation about sidecar containers
Is anybody working to fix this issue? If no, i can take it.
/assign
Feel free to involve me, if you need any help.
Sure, Thank you.
PR raised to fix the issue .
Also see
To learn more, you can read (but not plagiarize)
Hi, I also having this problem I tried to add restartPolicy as to under containers and init containers, but I get the same error. I do not got any errors for the restartPolicy, but and are gave the error mentioned at the top. Im using Minikube, and my CC: Your suggestions highly appriciatable
Looks like you are using 1.27, but this feature was in 1.28.
Thanks I updated my k8s Even though I can not use and in both places. ( and I put this marker in the above comment). It says,