# What's the main difference between hub\_connect\_url vs hub\_bind\_url?

**URL:** <https://discourse.jupyter.org/t/whats-the-main-difference-between-hub-connect-url-vs-hub-bind-url/3596>\
**Category:** General\
**Created:** [March 11, 2020, 11:05pm UTC](https://discourse.jupyter.org/t/whats-the-main-difference-between-hub-connect-url-vs-hub-bind-url/3596 "2020-03-11T23:05:06Z")\
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**Author:** ![minrk](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.jupyter.org/minrk/32/13_2.png) [@minrk](https://discourse.jupyter.org/u/minrk)\
**Post date:** [March 12, 2020, 8:34am UTC](https://discourse.jupyter.org/t/whats-the-main-difference-between-hub-connect-url-vs-hub-bind-url/3596/2 "2020-03-12T08:34:05Z")

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`hub_bind_url` is the URL passed to APIs such as `socket.listen`. This is what interface the socket is “bound to” or “listening on”. Most commonly, the ip has one of two values:

1. `127.0.0.1` for a single-host deployment. This will only work if the proxy and single-user servers are on the same host (or in the same container if you are using docker). This is the default value.
2. `0.0.0.0` for a multi-host (multi-container is multi-host) deployment, which means “all IPv4 interfaces”.

You can also specify a single LAN IP if you want to. This is typically useful in cluster scenarios where you want to avoid listening unnecessarily on publicly-accessible ips and only on the internal LAN.

In a container scenario, this will almost always want to be `"0.0.0.0"` because other containers are “external” from a networking perspective due to docker’s virtual networking/namespaces.

`hub_connect_url` is the URL passed to other entities, such as the proxy or single-user servers when they _connect_ to the Hub. This should use an ip or hostname that is connectable from the proxy and single-user servers. In Docker, this is often the name of the Hub container.

In docker, a common configuration would be:

```python
c.JupyterHub.hub_bind_url = "http://0.0.0.0:8081"
c.JupyterHub.hub_connect_url = "http://hub-container-name:8081"

```

because docker-networking makes a container’s name its hostname, connectable from other containers on a shared docker network. Importantly, docker networking does _not_ mean that binding on `0.0.0.0` is publicly accessible on the host. Only _within the docker network_ used by the Hub container.

The ports can (but typically do not) mismatch if you have routing layers in between, such as docker-swarm endpoints or kubernetes services, or other reverse-proxy layers. In those cases, you would use the listening port of the _intermediate service_ in `hub_connect_url` rather than the port the Hub binds on.

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