Chapter 310: Redundancy and the Whitelist

2:00 AM. The fluorescent tube in the rented apartment-cum-temporary server room hummed with a faint electrical buzz, a thin layer of dust clinging to the edges of the lampshade. Lin Chen sat on a folding chair, an A3 sheet of paper spread across his knees. His pencil scratched across the surface, leaving crisp lines. Core switch, dual 10-gigabit NICs, RAID 0 array, firewall policy zone, application servers. He drew slowly, annotating every connection with port numbers and VLAN IDs. The numbness in his left leg had crept past his knee, and his thigh muscles occasionally twitched out of control. He paused, pressing his knuckles hard into his quadriceps until the dull ache overpowered the sharp sting, then continued drawing.

The diagram didn’t need to be pretty; it just needed to be accurate. Capital verifies physical links, not art. He was used to breaking down complex problems into visual nodes, much like drawing grid squares with chalk on the living room floor as a child. Clear paths were the only basis for fault tolerance.

The door pushed open. Cold air rushed in, carrying the greasy smoke of the night market. Su Man walked in holding two black anti-static bags, her hair slightly tousled by the wind, dust settling on her shoulders. She set the bags on the table and unzipped them. Two second-hand enterprise-grade SSDs were revealed. Their labels were worn, the metal casings scratched, but the gold contacts were clean.

“Pulled from a decommissioned server. Power-on hours under three thousand. Seller guarantees three months.” Her voice was hoarse, bloodshot eyes betraying her fatigue. “The electronics market was about to close. Last shop. Haggled the price down, paid in cash.”

Lin Chen nodded, not asking for the exact price. He picked up a drive, running his fingertips over the connector. The metal was cold, the weight solid. He opened the chassis, removed the old mechanical drive, and slotted in the SSD. He tightened the screws with even pressure. The RAID card recognized it; array initialization began. A progress bar crawled slowly across the screen. He switched back to the terminal and typed in configuration commands. The screen scrolled, lines of characters falling into place.

“Network topology is done.” Lin Chen slid the A3 paper over. “Preliminary review tomorrow. The committee will verify the physical links on-site. The firewall whitelist will only allow the committee’s test IP range. Everything else gets DROPped. The demo environment will run on a direct intranet connection, bypassing public NAT.”

Su Man glanced at the diagram and nodded. “RAM disk is mounted. Two gigabytes of tmpfs. Log write latency is down to the microsecond level. But the async flush script is still being tuned; the concurrency parameters for rsync tend to deadlock.”

“Use ionice to lower the priority,” Lin Chen said. “During the demo, write only to memory. Flush to disk in the background afterward. If data is lost, we rerun. We don’t sacrifice real-time performance. Capital cares about the trajectory, not a safe.”

He sat back down at the computer, fingers resting on the keyboard. Terminal windows popped up one by one. iptables rules were entered line by line. sysctl parameters were adjusted: net.ipv4.tcp_max_syn_backlog, net.core.somaxconn, fs.file-max. Every number had been calculated. He didn’t need to show off; he just needed the system to hold under extreme pressure. Low-level parameters were static, but their combinations were dynamic. He was used to logging every crash threshold in his failure notebook; now, he was simply writing that experience into configuration files.

4:00 AM. Array initialization complete. Stress test scripts deployed. Locust configuration loaded. Lin Chen leaned back in his chair, closing his eyes. His breathing was shallow. Sensation in his left leg had vanished completely, as if it no longer belonged to him. He pulled a knee brace from the drawer and wrapped his calf and knee tightly with an elastic bandage. The bandage dug into his flesh, offering a false sense of support. He knew it was useless, but it could trick his nerves. Pain was a signal; numbness was a warning. He had to treat his body like an old server that needed to be throttled, keeping only the core processes running.

At the adjacent desk, Su Man was debugging the monitoring dashboard. The Grafana interface lit up, its curves starting at zero. The only sound in the room was the low-frequency hum of the spinning drives. Neither spoke. Silence was the norm. At this stage of a startup, words were superfluous. Only actions and results mattered. Two cans of cold instant coffee sat on the table, condensation beading on the aluminum. Lin Chen didn’t drink. An empty stomach kept him sharp.

8:50 AM. The three committee members arrived at the door right on time. Director Zhou, the auditor, and Representative Chen. Chen hadn’t brought a pen today, only a tablet. An invisible layer of pressure settled over the room.

“The link diagram,” Director Zhou said.

Lin Chen handed over the A3 sheet. The paper was flat, the annotations clear. Representative Chen glanced at it, said nothing, and walked to the server rack. He crouched down, tracing the Ethernet cable to the switch to verify the ports. His fingers lingered on the label for two seconds. “10-gigabit direct connection. No soft router in between.”

“Hard link,” Lin Chen replied. “Reduces hop count, minimizes latency jitter.”

Chen stood up and looked at Su Man. “Whitelist policy.”

Su Man brought up the terminal and typed iptables -L -n. The rule list scrolled. Only one ACCEPT rule pointed to the committee’s test IP. Everything else was DROP.

“You may begin,” Director Zhou said.

9:00 AM sharp. Locust launched. Concurrency climbed from one thousand. The curves rose steadily. CPU, memory, disk I/O, and network bandwidth—the four metrics pulsed in sync on the monitoring screen. Lin Chen stood by the rack, watching the temperature sensors. SSD at 42°C. NVMe cache drive at 38°C. RAM disk utilization at 15%. All normal.

Five thousand. Ten thousand. Median latency stabilized at 80 milliseconds. IOPS broke through 40,000.

“Ramp up the gradient faster,” Chen said, looking at his tablet. “Capital doesn’t care about slow burns. Jump straight to thirty thousand.”

Su Man’s fingers flew across the keyboard. Concurrency spiked instantly. The curves shot upward steeply. CPU usage hit 85%. Memory at 78%. Latency jumped to 120 milliseconds. Fan speeds increased, the noise drowning out conversation.

Lin Chen didn’t move. He stared at the log stream. tmpfs writes were normal. The async flush queue was backing up, but ionice was limiting disk contention. The system hadn’t frozen.

Twenty-five thousand. Tiny sawtooth patterns appeared on the latency curve. Not the disk, but a backplane bandwidth bottleneck in the network switch. Under sustained high concurrency, the queue depth on the 10-gigabit ports began to back up.

“Switch buffer is full,” Lin Chen said. “Adjust txqueuelen. Change it from 1000 to 5000. Do it now.”

Su Man executed the command. The terminal flickered. The sawtooth pattern flattened. Latency dropped back down.

Thirty thousand. The critical threshold. The curves oscillated at a high level. No cliff drops. No packet loss. Error rate at 0.01%.

“Log it,” Lin Chen said. “Maintain the sampling rate. Keep the raw logs.”

Ten minutes. Test over. Concurrency returned to zero. The fan noise faded. Only the faint sound of drives spinning down remained in the room.

Director Zhou signed the documents. The auditor cross-checked the data. Representative Chen put away his tablet and looked at Lin Chen. “Stress test passed. But the valuation adjustment settlement in the clause isn’t based on a single demo.” He paused. “Seventy-two hours. Continuous run. No downtime in between. No throttling. Data must sync in real-time to our monitoring nodes. Can you do it?”

“We can,” Lin Chen replied. His voice was flat.

Chen nodded, turned, and left. The door closed. Footsteps faded down the hallway.

Su Man let out a long breath, her shoulders slumping. “Passed the preliminary review.”

“Just the beginning.” Lin Chen sat down and unwrapped the bandage. Deep purple marks ringed his calf skin, the edges pale. He picked up the failure notebook from the table, turned to a fresh page, and wrote: Continuous 72-hour stress test. Real-time data sync. Capital monitoring node integration.

The pen tip paused. He added a line: Redundancy is not backup. It is fault tolerance.

His phone vibrated. Not the committee. A WeChat message from Zhao Qiming himself. Just one sentence:

Sync node is now active. Additionally, your API gateway rate-limiting policy will undergo a third-party stress injection this afternoon. Prepare in advance.

Lin Chen stared at the screen. Third-party stress injection. Not the committee’s test. Capital’s own probe. They weren’t just looking at the results; they wanted to see how the system reacted to unknown shocks.

He looked up at Su Man. “We need to change the gateway rules. Lower the rate-limiting threshold by twenty percent. Leave headroom.”

Su Man frowned. “Lowering it will false-positive normal requests. User experience will drop.”

“False positives are better than a cascade failure,” Lin Chen said. “Capital wants a controllable peak, not the true limit. We’ll give them the former. Advance the circuit breaker strategy. Failed requests will return a degraded page directly, no retries.”

He closed the notebook and picked up his jacket. His left foot still had no sensation when it hit the floor, but his gait had already adapted. Sunlight from outside streamed into the server room, dust motes drifting slowly in the beams. Next step: modify the gateway. The seventy-two hours had only just begun.