---
title: "Backup Hooks"
layout: docs
---

Velero supports executing commands in containers in pods during a backup.

## Backup Hooks

When performing a backup, you can specify one or more commands to execute in a container in a pod
when that pod is being backed up. The commands can be configured to run *before* any custom action
processing ("pre" hooks), or after all custom actions have been completed and any additional items
specified by custom action have been backed up ("post" hooks). Note that hooks are _not_ executed within a shell
on the containers.

There are two ways to specify hooks: annotations on the pod itself, and in the Backup spec.

### Specifying Hooks As Pod Annotations

You can use the following annotations on a pod to make Velero execute a hook when backing up the pod:

#### Pre hooks

* `pre.hook.backup.velero.io/container`
  * The container where the command should be executed. Defaults to the first container in the pod. Optional.
* `pre.hook.backup.velero.io/command`
  * The command to execute. If you need multiple arguments, specify the command as a JSON array, such as `["/usr/bin/uname", "-a"]`
* `pre.hook.backup.velero.io/on-error`
  * What to do if the command returns a non-zero exit code.  Defaults to Fail. Valid values are Fail and Continue. Optional.
* `pre.hook.backup.velero.io/timeout`
  * How long to wait for the command to execute. The hook is considered in error if the command exceeds the timeout. Defaults to 30s. Optional.


#### Post hooks

* `post.hook.backup.velero.io/container`
  * The container where the command should be executed. Defaults to the first container in the pod. Optional.
* `post.hook.backup.velero.io/command`
  * The command to execute. If you need multiple arguments, specify the command as a JSON array, such as `["/usr/bin/uname", "-a"]`
* `post.hook.backup.velero.io/on-error`
  * What to do if the command returns a non-zero exit code.  Defaults to Fail. Valid values are Fail and Continue. Optional.
* `post.hook.backup.velero.io/timeout`
  * How long to wait for the command to execute. The hook is considered in error if the command exceeds the timeout. Defaults to 30s. Optional.

### Specifying Hooks in the Backup Spec

Please see the documentation on the [Backup API Type][1] for how to specify hooks in the Backup
spec.

## Hook Example with fsfreeze

This examples walks you through using both pre and post hooks for freezing a file system. Freezing the
file system is useful to ensure that all pending disk I/O operations have completed prior to taking a snapshot.

This example uses [examples/nginx-app/with-pv.yaml][2]. Follow the [steps for your provider][3] to
setup this example.

### Annotations

The Velero [example/nginx-app/with-pv.yaml][2] serves as an example of adding the pre and post hook annotations directly
to your declarative deployment. Below is an example of what updating an object in place might look like.

```shell
kubectl annotate pod -n nginx-example -l app=nginx \
    pre.hook.backup.velero.io/command='["/sbin/fsfreeze", "--freeze", "/var/log/nginx"]' \
    pre.hook.backup.velero.io/container=fsfreeze \
    post.hook.backup.velero.io/command='["/sbin/fsfreeze", "--unfreeze", "/var/log/nginx"]' \
    post.hook.backup.velero.io/container=fsfreeze
```

Now test the pre and post hooks by creating a backup. You can use the Velero logs to verify that the pre and post
hooks are running and exiting without error.

```shell
velero backup create nginx-hook-test

velero backup get nginx-hook-test
velero backup logs nginx-hook-test | grep hookCommand
```

## Using Multiple Commands

To use multiple commands, wrap your target command in a shell and separate them with `;`, `&&`, or other shell conditional constructs.

```shell
    pre.hook.backup.velero.io/command='["/bin/bash", "-c", "echo hello > hello.txt && echo goodbye > goodbye.txt"]'
```


[1]: api-types/backup.md
[2]: https://github.com/vmware-tanzu/velero/blob/v1.7.0/examples/nginx-app/with-pv.yaml
[3]: cloud-common.md
