(topic-idle-culler)=

# Culling idle notebook servers

The idle culler automatically shuts down user notebook servers when they have
not been used for a certain time period, in order to reduce the total resource
usage on your JupyterHub.

The notebook server monitors activity internally
and notifies JupyterHub of recent activity at certain time intervals (the activity interval).
If JupyterHub has not been notified of any activity after a certain period (the idle timeout),
the server is considered to be _inactive (idle)_ and will be culled (shutdown).

The [idle culler](https://github.com/jupyterhub/jupyterhub-idle-culler) is a JupyterHub service that is installed and enabled by default in TLJH.
It can be configured using tljh-config. For advanced use-cases, like purging old user data,
the idle culler configuration can be extended beyond tljh-config options, using custom
[jupyterhub_config.py snippets](https://tljh.jupyter.org/en/latest/topic/escape-hatch.html?highlight=escape-hatch#extending-jupyterhub-config-py).

## Default settings

By default, JupyterHub will ping the user notebook servers every 10 min to check their
status. Every server found to be idle for more than 1 hour will be culled.

```python
services.cull.every = 600
services.cull.timeout = 3600
```

Because the servers don't have a maximum age set, an active server will not be shut down
regardless of how long it has been up and running.

```python
services.cull.max_age = 0
```

If after the culling process, there are users with no active notebook servers, by default,
the users will not be culled alongside their notebooks and will continue to exist.

```python
services.cull.users = False
```

If named servers are in use, they are not removed after being culled.

```python
services.cull.remove_named_servers = False
```

## Configuring the idle culler

The available configuration options are:

### Idle timeout

The idle timeout is the maximum time (in seconds) a server can be inactive before it
will be culled. The timeout can be configured using:

```bash
sudo tljh-config set services.cull.timeout <max-idle-sec-before-server-is-culled>
sudo tljh-config reload
```

### Idle check interval

The idle check interval represents how frequent (in seconds) the Hub will
check if there are any idle servers to cull. It can be configured using:

```bash
sudo tljh-config set services.cull.every <number-of-sec-this-check-is-done>
sudo tljh-config reload
```

### Maximum age

The maximum age sets the time (in seconds) a server should be running.
The servers that exceed the maximum age, will be culled even if they are active.
A maximum age of 0, will deactivate this option.
The maximum age can be configured using:

```bash
sudo tljh-config set services.cull.max_age <server-max-age>
sudo tljh-config reload
```

### Remove Named Servers

Remove named servers after they are shutdown. Only applies if named servers are
enabled on the hub installation:

```bash
sudo tljh-config set services.cull.remove_named_servers True
sudo tljh-config reload
```

### User culling

In addition to servers, it is also possible to cull the users. This is usually
suited for temporary-user cases such as _tmpnb_.
User culling can be activated using the following command:

```bash
sudo tljh-config set services.cull.users True
sudo tljh-config reload
```

### Concurrency

Deleting a lot of users at the same time can slow down the Hub.
The number of concurrent requests made to the Hub can be configured using:

```bash
sudo tljh-config set services.cull.concurrency <number-of-concurrent-hub-requests>
sudo tljh-config reload
```

Because TLJH it's used for a small number of users, the cases that may require to
modify the concurrency limit should be rare.

## Disabling the idle culler

The idle culling service is enabled by default. To disable it, use the following
command:

```bash
sudo tljh-config set services.cull.enabled False
sudo tljh-config reload
```
