Open WebUI: Failed to fetch from /ollama (cannot reach Ollama backend)

Environment: Open WebUI (Docker) connecting to a separately-running Ollama instance.

Severity: high — WebUI is unusable until reachable.

• Ollama bound to 127.0.0.1:11434 so the Open WebUI container can't reach it (containers see 127.0.0.1 as their own loopback)
• OLLAMA_BASE_URL env var in Open WebUI not set or pointing wrong
• Docker networks isolated (Open WebUI on bridge, Ollama on a different one)
• Firewall blocking 11434 between host and container
• Ollama not running at all

1. Bind Ollama to all interfaces so the container can reach it:

OLLAMA_HOST=0.0.0.0:11434 ollama serve
# Or persist via systemd:
sudo systemctl edit ollama
# [Service]
# Environment="OLLAMA_HOST=0.0.0.0:11434"
sudo systemctl daemon-reload && sudo systemctl restart ollama

2. Point Open WebUI at the host via OLLAMA_BASE_URL:

docker run -d --name open-webui \
  -p 3000:8080 \
  -e OLLAMA_BASE_URL=http://host.docker.internal:11434 \
  -v open-webui:/app/backend/data \
  --restart always \
  ghcr.io/open-webui/open-webui:main

On Linux without Docker Desktop, use the host's LAN IP (e.g. http://192.168.1.10:11434) or pass --add-host=host.docker.internal:host-gateway.

3. Run both on a shared bridge network (cleanest):

docker network create ai-net
docker run -d --network ai-net --name ollama -p 11434:11434 ollama/ollama
docker run -d --network ai-net --name open-webui \
  -e OLLAMA_BASE_URL=http://ollama:11434 \
  -p 3000:8080 ghcr.io/open-webui/open-webui:main

4. Test connectivity from inside the WebUI container:

docker exec -it open-webui curl http://host.docker.internal:11434/api/tags

A 200 with a JSON models array means the link is good.

5. Check firewall if on a Linux host with ufw/firewalld:

sudo ufw allow from 172.17.0.0/16 to any port 11434