Cannot get images from mnist
On https://huggingface.co/datasets/mnist, the images do not appear:

<img width="499" alt="Capture d’écran 2022-05-30 à 12 45 19" src="https://user-images.githubusercontent.com/1676121/170976397-cc283c45-afb5-43fa-9170-31689867deb7.png">

And the requests to the images return 403 or 404:

<img width="929" alt="Capture d’écran 2022-05-30 à 12 45 25" src="https://user-images.githubusercontent.com/1676121/170976411-43f7f348-2178-47e8-bd4f-71a415e25e22.png">

Their URLs are like:

https://huggingface.co/proxy-datasets-preview/assets/mnist/--/mnist/train/91/image/image.jpg
^does not work

Which should proxy to upstream URL:

https://datasets-server.huggingface.tech/assets/mnist/--/mnist/train/91/image/image.jpg
^works

See the nginx configuration: https://github.com/huggingface/conf/blob/bd698a91c615938b52477c25d72ba84d10af4c68/moonrise/nginx-moonrise.conf#L321-L328

Looking at the nginx logs on moonrise (`sudo grep proxy-datasets-preview /var/log/nginx/error.log`) we get a lot of `Connection timed out` errors:

```
2022/05/30 12:41:41 [error] 687523#687523: *867222115 upstream timed out (110: Connection timed out) while connecting to upstream, client: 172.30.1.33, server: huggingface.co, request: "GET /proxy-datasets-preview/assets/mnist/--/mnist/train/91/image/image.jpg HTTP/1.1", upstream: "https://35.175.164.194:443/assets/mnist/--/mnist/train/91/image/image.jpg", host: "huggingface.co"
```

This means that moonrise does not seem able to access the datasets-server.huggingface.co server.

Launching curl from the moonrise server with the domain works:

```
curl https://datasets-server.huggingface.tech/assets/mnist/--/mnist/train/91/image/image.jpg > image.jpg
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   561  100   561    0     0  31166      0 --:--:-- --:--:-- --:--:-- 31166
```

But not with the IP reported in the logs (it timeouts):

```
hf@moonrise:/tmp$ curl https://35.175.164.194:443/assets/mnist/--/mnist/train/91/image/image.jpg > image.jpg
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:01:10 --:--:--     0
```

The IP resolved for datasets-server.huggingface.tech:

```
hf@moonrise:/tmp$ dig datasets-server.huggingface.tech

; <<>> DiG 9.16.1-Ubuntu <<>> datasets-server.huggingface.tech
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48677
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;datasets-server.huggingface.tech. IN   A

;; ANSWER SECTION:
datasets-server.huggingface.tech. 13 IN A       34.194.63.218
datasets-server.huggingface.tech. 13 IN A       52.204.14.32
datasets-server.huggingface.tech. 13 IN A       184.72.186.69
datasets-server.huggingface.tech. 13 IN A       50.16.88.70
datasets-server.huggingface.tech. 13 IN A       34.236.116.183
datasets-server.huggingface.tech. 13 IN A       34.239.243.182

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon May 30 12:52:46 CEST 2022
;; MSG SIZE  rcvd: 157
```
Cannot get images from mnist: On https://huggingface.co/datasets/mnist, the images do not appear:

<img width="499" alt="Capture d’écran 2022-05-30 à 12 45 19" src="https://user-images.githubusercontent.com/1676121/170976397-cc283c45-afb5-43fa-9170-31689867deb7.png">

And the requests to the images return 403 or 404:

<img width="929" alt="Capture d’écran 2022-05-30 à 12 45 25" src="https://user-images.githubusercontent.com/1676121/170976411-43f7f348-2178-47e8-bd4f-71a415e25e22.png">

Their URLs are like:

https://huggingface.co/proxy-datasets-preview/assets/mnist/--/mnist/train/91/image/image.jpg
^does not work

Which should proxy to upstream URL:

https://datasets-server.huggingface.tech/assets/mnist/--/mnist/train/91/image/image.jpg
^works

See the nginx configuration: https://github.com/huggingface/conf/blob/bd698a91c615938b52477c25d72ba84d10af4c68/moonrise/nginx-moonrise.conf#L321-L328

Looking at the nginx logs on moonrise (`sudo grep proxy-datasets-preview /var/log/nginx/error.log`) we get a lot of `Connection timed out` errors:

```
2022/05/30 12:41:41 [error] 687523#687523: *867222115 upstream timed out (110: Connection timed out) while connecting to upstream, client: 172.30.1.33, server: huggingface.co, request: "GET /proxy-datasets-preview/assets/mnist/--/mnist/train/91/image/image.jpg HTTP/1.1", upstream: "https://35.175.164.194:443/assets/mnist/--/mnist/train/91/image/image.jpg", host: "huggingface.co"
```

This means that moonrise does not seem able to access the datasets-server.huggingface.co server.

Launching curl from the moonrise server with the domain works:

```
curl https://datasets-server.huggingface.tech/assets/mnist/--/mnist/train/91/image/image.jpg > image.jpg
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   561  100   561    0     0  31166      0 --:--:-- --:--:-- --:--:-- 31166
```

But not with the IP reported in the logs (it timeouts):

```
hf@moonrise:/tmp$ curl https://35.175.164.194:443/assets/mnist/--/mnist/train/91/image/image.jpg > image.jpg
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:01:10 --:--:--     0
```

The IP resolved for datasets-server.huggingface.tech:

```
hf@moonrise:/tmp$ dig datasets-server.huggingface.tech

; <<>> DiG 9.16.1-Ubuntu <<>> datasets-server.huggingface.tech
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48677
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;datasets-server.huggingface.tech. IN   A

;; ANSWER SECTION:
datasets-server.huggingface.tech. 13 IN A       34.194.63.218
datasets-server.huggingface.tech. 13 IN A       52.204.14.32
datasets-server.huggingface.tech. 13 IN A       184.72.186.69
datasets-server.huggingface.tech. 13 IN A       50.16.88.70
datasets-server.huggingface.tech. 13 IN A       34.236.116.183
datasets-server.huggingface.tech. 13 IN A       34.239.243.182

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon May 30 12:52:46 CEST 2022
;; MSG SIZE  rcvd: 157
```