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Cleanup container probes task (#18233)

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* Fix markdown for sample output

Don't highlight this sample output as if it's Bourne shell code.

* Tweak capitalization

- Pod is an API object type
- Container exists in the Kubernetes API, but you can't:
  kubectl get container
- Socket isn't an API object type

* Pin source to relevant release

Handle case where sample Golang server changes in master branch post
release.

* Tweak page wording

- Reword a heading in What's Next to explain the links
- explain context for a probe
This commit is contained in:
Tim Bannister
2020-03-16 05:24:35 +00:00
committed by GitHub
parent b2e7dee806
commit 6f48108c95
1 changed files with 31 additions and 31 deletions
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content/en/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes.md
+31 -31
View File
@@ -6,20 +6,20 @@ weight: 110
{{% capture overview %}} {{% capture overview %}}
This page shows how to configure liveness, readiness and startup probes for Containers. This page shows how to configure liveness, readiness and startup probes for containers.
The [kubelet](/docs/admin/kubelet/) uses liveness probes to know when to The [kubelet](/docs/admin/kubelet/) uses liveness probes to know when to
restart a Container. For example, liveness probes could catch a deadlock, restart a container. For example, liveness probes could catch a deadlock,
where an application is running, but unable to make progress. Restarting a where an application is running, but unable to make progress. Restarting a
Container in such a state can help to make the application more available container in such a state can help to make the application more available
despite bugs. despite bugs.
The kubelet uses readiness probes to know when a Container is ready to start The kubelet uses readiness probes to know when a container is ready to start
accepting traffic. A Pod is considered ready when all of its Containers are ready. accepting traffic. A Pod is considered ready when all of its containers are ready.
One use of this signal is to control which Pods are used as backends for Services. One use of this signal is to control which Pods are used as backends for Services.
When a Pod is not ready, it is removed from Service load balancers. When a Pod is not ready, it is removed from Service load balancers.
The kubelet uses startup probes to know when a Container application has started. The kubelet uses startup probes to know when a container application has started.
If such a probe is configured, it disables liveness and readiness checks until If such a probe is configured, it disables liveness and readiness checks until
it succeeds, making sure those probes don't interfere with the application startup. it succeeds, making sure those probes don't interfere with the application startup.
This can be used to adopt liveness checks on slow starting containers, avoiding them This can be used to adopt liveness checks on slow starting containers, avoiding them
@@ -41,27 +41,27 @@ Many applications running for long periods of time eventually transition to
broken states, and cannot recover except by being restarted. Kubernetes provides broken states, and cannot recover except by being restarted. Kubernetes provides
liveness probes to detect and remedy such situations. liveness probes to detect and remedy such situations.
In this exercise, you create a Pod that runs a Container based on the In this exercise, you create a Pod that runs a container based on the
`k8s.gcr.io/busybox` image. Here is the configuration file for the Pod: `k8s.gcr.io/busybox` image. Here is the configuration file for the Pod:
{{< codenew file="pods/probe/exec-liveness.yaml" >}} {{< codenew file="pods/probe/exec-liveness.yaml" >}}
In the configuration file, you can see that the Pod has a single Container. In the configuration file, you can see that the Pod has a single `Container`.
The `periodSeconds` field specifies that the kubelet should perform a liveness The `periodSeconds` field specifies that the kubelet should perform a liveness
probe every 5 seconds. The `initialDelaySeconds` field tells the kubelet that it probe every 5 seconds. The `initialDelaySeconds` field tells the kubelet that it
should wait 5 second before performing the first probe. To perform a probe, the should wait 5 second before performing the first probe. To perform a probe, the
kubelet executes the command `cat /tmp/healthy` in the Container. If the kubelet executes the command `cat /tmp/healthy` in the target container. If the
command succeeds, it returns 0, and the kubelet considers the Container to be alive and command succeeds, it returns 0, and the kubelet considers the container to be alive and
healthy. If the command returns a non-zero value, the kubelet kills the Container healthy. If the command returns a non-zero value, the kubelet kills the container
and restarts it. and restarts it.
When the Container starts, it executes this command: When the container starts, it executes this command:
```shell ```shell
/bin/sh -c "touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600" /bin/sh -c "touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600"
``` ```
For the first 30 seconds of the Container's life, there is a `/tmp/healthy` file. For the first 30 seconds of the container's life, there is a `/tmp/healthy` file.
So during the first 30 seconds, the command `cat /tmp/healthy` returns a success So during the first 30 seconds, the command `cat /tmp/healthy` returns a success
code. After 30 seconds, `cat /tmp/healthy` returns a failure code. code. After 30 seconds, `cat /tmp/healthy` returns a failure code.
@@ -79,7 +79,7 @@ kubectl describe pod liveness-exec
The output indicates that no liveness probes have failed yet: The output indicates that no liveness probes have failed yet:
```shell ```
FirstSeen LastSeen Count From SubobjectPath Type Reason Message FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ ------- --------- -------- ----- ---- ------------- -------- ------ -------
24s 24s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0 24s 24s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
@@ -98,7 +98,7 @@ kubectl describe pod liveness-exec
At the bottom of the output, there are messages indicating that the liveness At the bottom of the output, there are messages indicating that the liveness
probes have failed, and the containers have been killed and recreated. probes have failed, and the containers have been killed and recreated.
```shell ```
FirstSeen LastSeen Count From SubobjectPath Type Reason Message FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ ------- --------- -------- ----- ---- ------------- -------- ------ -------
37s 37s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0 37s 37s 1 {default-scheduler } Normal Scheduled Successfully assigned liveness-exec to worker0
@@ -109,7 +109,7 @@ FirstSeen LastSeen Count From SubobjectPath Type
2s 2s 1 {kubelet worker0} spec.containers{liveness} Warning Unhealthy Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory 2s 2s 1 {kubelet worker0} spec.containers{liveness} Warning Unhealthy Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory
``` ```
Wait another 30 seconds, and verify that the Container has been restarted: Wait another 30 seconds, and verify that the container has been restarted:
```shell ```shell
kubectl get pod liveness-exec kubectl get pod liveness-exec
@@ -117,7 +117,7 @@ kubectl get pod liveness-exec
The output shows that `RESTARTS` has been incremented: The output shows that `RESTARTS` has been incremented:
```shell ```
NAME READY STATUS RESTARTS AGE NAME READY STATUS RESTARTS AGE
liveness-exec 1/1 Running 1 1m liveness-exec 1/1 Running 1 1m
``` ```
@@ -130,23 +130,23 @@ image.
{{< codenew file="pods/probe/http-liveness.yaml" >}} {{< codenew file="pods/probe/http-liveness.yaml" >}}
In the configuration file, you can see that the Pod has a single Container. In the configuration file, you can see that the Pod has a single container.
The `periodSeconds` field specifies that the kubelet should perform a liveness The `periodSeconds` field specifies that the kubelet should perform a liveness
probe every 3 seconds. The `initialDelaySeconds` field tells the kubelet that it probe every 3 seconds. The `initialDelaySeconds` field tells the kubelet that it
should wait 3 seconds before performing the first probe. To perform a probe, the should wait 3 seconds before performing the first probe. To perform a probe, the
kubelet sends an HTTP GET request to the server that is running in the Container kubelet sends an HTTP GET request to the server that is running in the container
and listening on port 8080. If the handler for the server's `/healthz` path and listening on port 8080. If the handler for the server's `/healthz` path
returns a success code, the kubelet considers the Container to be alive and returns a success code, the kubelet considers the container to be alive and
healthy. If the handler returns a failure code, the kubelet kills the Container healthy. If the handler returns a failure code, the kubelet kills the container
and restarts it. and restarts it.
Any code greater than or equal to 200 and less than 400 indicates success. Any Any code greater than or equal to 200 and less than 400 indicates success. Any
other code indicates failure. other code indicates failure.
You can see the source code for the server in You can see the source code for the server in
[server.go](https://github.com/kubernetes/kubernetes/blob/master/test/images/agnhost/liveness/server.go). [server.go](https://github.com/kubernetes/kubernetes/blob/{{< param "githubbranch" >}}/test/images/agnhost/liveness/server.go).
For the first 10 seconds that the Container is alive, the `/healthz` handler For the first 10 seconds that the container is alive, the `/healthz` handler
returns a status of 200. After that, the handler returns a status of 500. returns a status of 200. After that, the handler returns a status of 500.
```go ```go
@@ -162,9 +162,9 @@ http.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
}) })
``` ```
The kubelet starts performing health checks 3 seconds after the Container starts. The kubelet starts performing health checks 3 seconds after the container starts.
So the first couple of health checks will succeed. But after 10 seconds, the health So the first couple of health checks will succeed. But after 10 seconds, the health
checks will fail, and the kubelet will kill and restart the Container. checks will fail, and the kubelet will kill and restart the container.
To try the HTTP liveness check, create a Pod: To try the HTTP liveness check, create a Pod:
@@ -173,21 +173,21 @@ kubectl apply -f https://k8s.io/examples/pods/probe/http-liveness.yaml
``` ```
After 10 seconds, view Pod events to verify that liveness probes have failed and After 10 seconds, view Pod events to verify that liveness probes have failed and
the Container has been restarted: the container has been restarted:
```shell ```shell
kubectl describe pod liveness-http kubectl describe pod liveness-http
``` ```
In releases prior to v1.13 (including v1.13), if the environment variable In releases prior to v1.13 (including v1.13), if the environment variable
`http_proxy` (or `HTTP_PROXY`) is set on the node where a pod is running, `http_proxy` (or `HTTP_PROXY`) is set on the node where a Pod is running,
the HTTP liveness probe uses that proxy. the HTTP liveness probe uses that proxy.
In releases after v1.13, local HTTP proxy environment variable settings do not In releases after v1.13, local HTTP proxy environment variable settings do not
affect the HTTP liveness probe. affect the HTTP liveness probe.
## Define a TCP liveness probe ## Define a TCP liveness probe
A third type of liveness probe uses a TCP Socket. With this configuration, the A third type of liveness probe uses a TCP socket. With this configuration, the
kubelet will attempt to open a socket to your container on the specified port. kubelet will attempt to open a socket to your container on the specified port.
If it can establish a connection, the container is considered healthy, if it If it can establish a connection, the container is considered healthy, if it
can’t it is considered a failure. can’t it is considered a failure.
@@ -197,7 +197,7 @@ can’t it is considered a failure.
As you can see, configuration for a TCP check is quite similar to an HTTP check. As you can see, configuration for a TCP check is quite similar to an HTTP check.
This example uses both readiness and liveness probes. The kubelet will send the This example uses both readiness and liveness probes. The kubelet will send the
first readiness probe 5 seconds after the container starts. This will attempt to first readiness probe 5 seconds after the container starts. This will attempt to
connect to the `goproxy` container on port 8080. If the probe succeeds, the pod connect to the `goproxy` container on port 8080. If the probe succeeds, the Pod
will be marked as ready. The kubelet will continue to run this check every 10 will be marked as ready. The kubelet will continue to run this check every 10
seconds. seconds.
@@ -351,7 +351,7 @@ port to perform the check. The kubelet sends the probe to the pod’s IP address
unless the address is overridden by the optional `host` field in `httpGet`. If unless the address is overridden by the optional `host` field in `httpGet`. If
`scheme` field is set to `HTTPS`, the kubelet sends an HTTPS request skipping the `scheme` field is set to `HTTPS`, the kubelet sends an HTTPS request skipping the
certificate verification. In most scenarios, you do not want to set the `host` field. certificate verification. In most scenarios, you do not want to set the `host` field.
Here's one scenario where you would set it. Suppose the Container listens on 127.0.0.1 Here's one scenario where you would set it. Suppose the container listens on 127.0.0.1
and the Pod's `hostNetwork` field is true. Then `host`, under `httpGet`, should be set and the Pod's `hostNetwork` field is true. Then `host`, under `httpGet`, should be set
to 127.0.0.1. If your pod relies on virtual hosts, which is probably the more common to 127.0.0.1. If your pod relies on virtual hosts, which is probably the more common
case, you should not use `host`, but rather set the `Host` header in `httpHeaders`. case, you should not use `host`, but rather set the `Host` header in `httpHeaders`.
@@ -367,7 +367,7 @@ to resolve it.
* Learn more about * Learn more about
[Container Probes](/docs/concepts/workloads/pods/pod-lifecycle/#container-probes). [Container Probes](/docs/concepts/workloads/pods/pod-lifecycle/#container-probes).
### Reference You can also read the API references for:
* [Pod](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#pod-v1-core) * [Pod](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#pod-v1-core)
* [Container](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#container-v1-core) * [Container](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#container-v1-core)