How to Pinpoint and Resolve Packet Loss in Cloud‑Native Deployments with SysOM

As enterprises migrate core services to the cloud, reliable network communication becomes essential for business continuity. Packet loss directly impacts system stability: mild loss can cause intermittent failures, while severe loss may trigger health‑check failures, ping timeouts, and service denial.

Background

A customer deploying a distributed cluster in a new region encountered network packet loss, leading to node communication interruptions and stalled deployments. Alibaba Cloud CloudMonitor 2.0’s SysOM intelligent diagnosis identified the fault within hours, enabling rapid business recovery.

Scenario 1 – Quick Problem Definition

During ACK (Alibaba Cloud Kubernetes Service) cluster deployment, health‑check SYN packets from the SLB reached the ECS instance but no ACK was returned, causing health‑check failures. Initial checks ruled out iptables differences, shifting focus to potential kernel‑level packet loss.

Using the OS console, engineers captured traffic on eth0 with tcpdump. The capture showed SYN packets arriving from the SLB health‑check subnet, but no ACK responses.

Check iptables Rules

Comparison of iptables configurations between healthy and problematic hosts showed identical policies, confirming iptables was not the cause.

Investigate Kernel Packet Loss

SysOM’s kernel‑level network diagnostics were run via the OS console. The report indicated no known packet‑loss events, effectively ruling out kernel drops.

Examine Drivers and Hooks

Further analysis revealed numerous sched_cls hooks injected by a network component. After confirming with the ACK R&D team that these hooks originated from a specific module, the component was unloaded, instantly restoring health‑check functionality.

Scenario 2 – Precise Issue Localization

Another customer reported that port 1678 could not be reached via telnet, while port 22 worked. All services were listening, and iptables showed no restrictive rules. The suspicion shifted to hidden netfilter mechanisms.

SysOM’s network‑diagnosis workflow was executed, producing a report that highlighted a drop rule in nftables targeting port 1678. The rule was removed, and connectivity to the port was restored.

General Troubleshooting Steps

Run SysOM’s packet‑loss diagnosis and review the generated report for explicit root‑cause hints.

If the kernel is clean, verify the presence of unexpected security modules or hooks by comparing with a baseline system.

Inspect iptables and nftables configurations for drop rules affecting the affected ports or protocols.

When necessary, employ advanced tools such as funcgraph or BPF tracing to pinpoint loss points in the network stack.

Following these steps typically enables operators to identify and resolve most packet‑loss issues in cloud‑native environments, turning complex network failures into manageable tasks.