Understanding OVHcloud Architecture
Core Infrastructure Elements
OVHcloud services rely on key building blocks:
- Public Cloud Instances: Scalable VMs with access to OpenStack APIs
- VRACK: Virtual private network for interconnecting resources securely
- Load Balancer as a Service (LBaaS): For distributing traffic in HA setups
- Bare-metal Servers: Dedicated machines with full hardware control
Misconfigurations in these layers—particularly around networking and DNS—can trigger cascading failures.
Common Operational Failures
1. VRACK Misconfiguration and Loss of Connectivity
Improperly assigned interfaces in VRACK can isolate instances from private or hybrid networks. Often, IPs are not routed correctly, causing:
Destination Host Unreachable No route to host Timeout on private IP ping
This typically stems from missing routes or VLAN binding errors in the OVH Manager portal.
2. HA IP Failover Issues
Failover IPs are common for high availability. Incorrect configuration of netplan or legacy ifupdown tools on Ubuntu/Debian leads to failover IPs not binding post-reboot or post-failover:
RTNETLINK answers: File exists ip route add failed
Some systems require custom routes and ARP settings via arping to fully activate the failover IP.
3. Reboot-Induced Network Isolation
Rebooting an instance may cause network interfaces to reset incorrectly if cloud-init or DHCP client settings are corrupted. This often affects bare-metal servers with custom ISO installs.
4. DNS Resolution Failures from OVH Resolvers
OVH default resolvers may sporadically timeout in high-traffic regions. Applications depending on DNS resolution (e.g., microservices, CI/CD pipelines) stall or fail.
Diagnostics and Tools
Network Tracing and VRACK Checks
Run interface and routing diagnostics:
ip a ip r ethtool -i eth0
Confirm VRACK VLAN ID bindings via OVH Manager → Network Interfaces. Use tcpdump to verify traffic on tagged interfaces.
Failover IP Binding Verification
Check that the correct MAC and subnet routing is applied. Use:
ip addr add {failover_ip}/32 dev eth0
>arping -c 3 -A -I eth0 {gateway_ip}
Ensure that scripts used to reassign failover IPs run at boot (e.g., systemd unit or rc.local fallback).
Cloud-Init and DHCP Logs
Review logs to trace IP assignment failures:
journalctl -u cloud-init cat /var/log/syslog | grep dhclient
Misconfigured DHCP timeouts or improperly applied network configs will appear here.
DNS Debugging
Validate with:
dig @127.0.0.1 www.ovh.com dig @resolver1.opendns.com myip.opendns.com
If OVH resolvers are flaky, switch to Cloudflare (1.1.1.1) or Google (8.8.8.8) for improved stability.
Step-by-Step Fixes
1. Reassign VRACK Interface Correctly
Use the OVH Manager or API to detach and reattach the interface to the correct VRACK. Ensure matching VLANs and security group rules are in place.
2. Configure Failover IP on Boot
On Ubuntu:
network:
version: 2
ethernets:
eth0:
dhcp4: true
addresses: [FAILOVER_IP/32]
gateway4: GATEWAY_IP
nameservers:
addresses: [8.8.8.8, 1.1.1.1]
Also include post-boot script for arping to advertise the new IP.
3. Rebuild Netplan or Networking Service
If boot fails with no network:
sudo netplan generate && sudo netplan apply
Or restart systemd-networkd for older systems:
sudo systemctl restart systemd-networkd
4. Replace DNS Temporarily
Edit /etc/resolv.conf or systemd-resolved config:
nameserver 1.1.1.1 nameserver 8.8.8.8
Persist settings in /etc/systemd/resolved.conf if using systemd-resolved.
Best Practices and Architectural Recommendations
Use Configuration Management for Network Profiles
Automate failover and VRACK setup using Ansible or Terraform scripts. This ensures idempotent setup across nodes and prevents drift.
Deploy Redundant DNS Resolvers
Run local DNS resolvers with upstream fallback to avoid regional resolver outages. This improves resilience of microservices dependent on name resolution.
Centralize Network Monitoring
Use tools like Zabbix, Prometheus, or OVHcloud's own metrics to monitor VRACK interface health, latency, and failover events.
Leverage Service IP Groups
Use OVHcloud's IPFO ranges and group-based routing to automate failover IP reassignment across VMs for high availability setups.
Conclusion
While OVHcloud offers flexible infrastructure, its VRACK and IP failover mechanisms introduce unique operational challenges in production. Mastery of OVH-specific tooling, automation of network configuration, and proactive DNS and routing validation are essential to maintain uptime in critical systems. With careful architecture and robust monitoring, teams can harness the full potential of OVHcloud while minimizing risk during network transitions or host reboots.
FAQs
1. Why does my instance lose connectivity after reboot?
This often occurs due to missing VRACK route bindings or incorrect failover IP configurations not reapplied on boot. Check netplan or network scripts.
2. How do I test if a failover IP is working?
Use ip a to verify IP binding, and arping to announce it to the switch. Ping from an external host to confirm reachability.
3. Can I use custom DNS resolvers in OVHcloud?
Yes. OVH allows overriding default resolvers. It’s recommended to use resilient resolvers like Cloudflare or Google in production environments.
4. Is VRACK traffic encrypted?
No. VRACK offers Layer 2 isolation but not encryption. Use TLS or VPN tunnels over VRACK for sensitive data transmission.
5. How can I automate OVHcloud networking setup?
Use OVH APIs or Terraform OVH provider modules to automate VRACK assignment, IP routing, and instance provisioning with configuration management tools.