> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Liveness Probes
> Liveness probes in Kubernetes check container health, automatically restarting unresponsive applications to maintain availability without manual intervention.
In Kubernetes, **liveness probes** periodically check whether a container is still running correctly. If a probe fails, Kubernetes kills and restarts the container, restoring application availability without manual intervention.
## Basic Docker Behavior
When you run an application in Docker, any crash stops the container until you restart it manually:
```bash theme={null}
docker run nginx
```
If the `nginx` process crashes:
```bash theme={null}
docker ps -a
```
```text theme={null}
CONTAINER ID IMAGE CREATED STATUS PORTS
45aacca36850 nginx 43 seconds ago Exited (1) 41 seconds ago
```
## Kubernetes Automatic Restarts
Kubernetes continuously monitors container exit codes and restarts crashed containers automatically:
```bash theme={null}
kubectl run nginx --image=nginx
kubectl get pods
```
```text theme={null}
NAME READY STATUS RESTARTS AGE
nginx-pod 0/1 Completed 1 1d
```
Each time the container exits unexpectedly, the **RESTARTS** count increments. However, if an application stays running but becomes unresponsive (for example, trapped in an infinite loop), Kubernetes still considers it healthy—until you explicitly tell it how to check deeper.
Without a liveness probe, Kubernetes **cannot** detect hung or unresponsive applications that have not exited.
## Introducing Liveness Probes
A **liveness probe** defines how Kubernetes determines container health. You choose one of three probe types:
| Probe Type | Use Case | Configuration Snippet |
| ---------- | ---------------------- | -------------------------------- |
| HTTP GET | Web services | `httpGet` with `path` and `port` |
| TCP Socket | TCP-based protocols | `tcpSocket` with `port` |
| Exec | Custom commands/checks | `exec` with a `command` array |
When a container fails its liveness probe, Kubernetes restarts it automatically.
### HTTP Liveness Probe Example
```yaml theme={null}
apiVersion: v1
kind: Pod
metadata:
name: simple-webapp
spec:
containers:
- name: simple-webapp
image: simple-webapp
ports:
- containerPort: 8080
livenessProbe:
httpGet:
path: /api/healthy
port: 8080
initialDelaySeconds: 15
periodSeconds: 10
failureThreshold: 3
```
Explanation:
1. `initialDelaySeconds: 15`\
Waits 15 seconds before the first health check.
2. `periodSeconds: 10`\
Probes every 10 seconds.
3. `failureThreshold: 3`\
Restarts the container after three consecutive failures.
## Additional Probe Examples
Below are more probe configurations—applicable to both **liveness** and **readiness** probes:
```yaml theme={null}
readinessProbe:
httpGet:
path: /api/ready
port: 8080
initialDelaySeconds: 10
periodSeconds: 5
failureThreshold: 8
---
readinessProbe:
tcpSocket:
port: 3306
---
readinessProbe:
exec:
command:
- cat
- /app/is_ready
```
By leveraging these probe types, you ensure Kubernetes can detect both crashed and unresponsive containers, automatically restoring service availability.
## Links and References
* [Kubernetes Probes Documentation](https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/)
* [Docker CLI Reference](https://docs.docker.com/engine/reference/commandline/cli/)
* [Pods in Kubernetes Basics](https://kubernetes.io/docs/concepts/workloads/pods/pod/)