-
Notifications
You must be signed in to change notification settings - Fork 14.4k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Merge pull request #43346 from T-Lakshmi/sidecar-container
Add a new concept page for Sidecar containers
- Loading branch information
Showing
3 changed files
with
180 additions
and
55 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
126 changes: 126 additions & 0 deletions
126
content/en/docs/concepts/workloads/pods/sidecar-containers.md
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,126 @@ | ||
| --- | ||
| 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/). |