yoursunny blog
computer, Internet, and life

yoursunny.com Disaster Recovery Plan: 104 Minutes Downtime, No Tears

Junxiao Shi

The OVH fire taught us the importance of having a disaster recovery plan for your website and online services. In 2017, I rebuilt yoursunny.com and moved everything from configuration to content into git repositories. One of the reasons was that, the git repository could serve as a backup of the website, so that I can recover the site from a data loss.

uptime last 24 hours, vps4 server, yoursunny.com website

Today, I was forced to execute (part of) my disaster recovery plan. The result was: website is successfully recovered after 1 hour and 44 minutes of downtime.

🟥 Down

When I waked up this morning, there were several alert emails from UptimeRobot telling me that my website was down, up, down, and up again. At the same time, I also received alerts that the VPS hosting the website was not responding to ping. I ignored those alerts, thinking that they would resolve itself in a few minutes.

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Ranked 10000 in Code Jam 2021 Qualification, Perl + Scala + Dart

Junxiao Shi

I spent the Saturday competing in Google Code Jam 2021 qualification round, and earned a well-rounded rank: exactly 10000.

yoursunny rank 10000

Code Jam is about Algorithms

My first time competing in Code Jam was 2012. I heard about Code Jam earlier that year, from a flyer posted by the ACM student chapter at University of Arizona. Since then, I participated in Code Jam every year, and 2021 is my 10th year competing in Code Jam.

Code Jam isn't about code or jam, but about mathematics and algorithms. Although I'm a good network programmer and write a lot of production quality code, I struggle at algorithms especially when I'm under a time pressure. Nevertheless, I continued competing in this annual event, so that I can remember the last bits of algorithms, and occasionally learn a few new tricks by reading through the post-round analyses.

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NDN Video Streaming over QUIC

Junxiao Shi

NDN over WebSockets == TCP over TCP

Named Data Networking (NDN) was first ported to web browser environment in 2012. At that time, a browser-based JavaScript application can communicate with the Internet via either XMLHTTPRequest or WebSocket. Feeling that WebSocket is a better match for the NDN implementation at the time, I wrote the initial code for a CCNx WebSocket proxy.

Web applications would connect to this proxy over TCP, negotiate a WebSocket connection, and send NDN packets in WebSocket frames. The proxy then decapsulates these frames, and delivers the NDN packets to ccnd forwarder over TCP.

NDN-over-WebSockets survived multiple protocol changes over the years, and made its way into the NDN Forwarding Daemon (NFD). It worked fine for simple NDN web applications, such as status pages and text chat, and even file retrievals.

Recently, with the rise of video streaming on the NDN testbed, congestion control functionality starts to show up in NDN libraries. Then, a question popped into my mind: WebSockets run over TCP, and NDN congestion control algorithms are largely borrowed from TCP, would this cause any problems?

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OVH Strasbourg: Halt and Catch Fire, Data Uploaded to the Cloud

Junxiao Shi

2021-03-10, an OVH Cloud data center in Strasbourg, France caught on fire. Thousands of servers have been destroyed by fire. Thousands more are currently unavailable due to power cut, and will remain offline for several more days.

Data stored in those servers have been uploaded to the cloud via black smoke.

a building is burning with black smoke rising to the sky

According to Hacker News, a Dev mistakenly invoked the Halt and Catch Fire instruction on an Uninterrupted Power Supply unit, causing this incident.

Chairman of OVH cloud advised clients to activate their disaster recovery plans, such as restoring off-site backups to a new cloud server. Some clients are crying because they did not have backups, or they stored their backups on another machine in the same data center. Other clients experienced no downtime because they designed their systems for datacenter scale redundancy.

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漫步在北京 (下) | Wandering in Beijing (2)

Junxiao Shi

北京历史悠久，景点众多，一篇文章写不下。 所以，接着上篇，我来继续回顾我在北京看到的风景名胜。

Beijing has a long history and more attractions than what I can fit in one article. Following the previous part, let me continue revisiting what I've experienced in Beijing.

北京的长城 | Great Wall

万里长城是中国古代建造的最为宏大的工程之一，也是中华民族精神的象征。 长城在春秋战国时期即已修筑，不过北京附近的长城大多数是明代建造的。 八达岭是北京最著名、交通比较方便的一段长城。 我在2013年6月16日游览了八达岭长城。

Great Wall of China is one of the most magnificent projects in ancient China. It has existed since more than 2500 years ago, but most remaining Great Wall sections near Beijing were built in the Ming Dynasty. Badaling is the most visited section of Great Wall because it's conveniently accessible by public transit. I visited Badaling on 16 June 2013.

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Rename WiFi Interface on Ubuntu 20.04

Junxiao Shi

During an experiment, I need to use three WiFi interfaces on a Raspberry Pi running Ubuntu 20.04. In addition to Raspberry Pi's internal WiFi interface, I added two USB WiFi adapters. Three network interfaces showed up in the system (ip link command), and they are named wlan0, wlan1, and wlan2 by default.

I often need to capture packets with tcpdump, and I often have to be type these interface names manually. It isn't easy to remember the purpose of each network interface, so I wanted to rename the interfaces to reflect their role in my application. However, this isn't as easy as it sounds.

🚫 Netplan

Ubuntu 20.04 configures network interfaces using Netplan, so my first thought was: I can write a Netplan configuration that matches network interfaces with their MAC addresses, and assigns the desired name to each network interface.

The config file would look like this:

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漫步在北京 (上) | Wandering in Beijing (1)

Junxiao Shi

北京是中国的首都，我在2010、2011、2013年去过三次。 在2021年第一次“虚拟旅游”中，我来回顾一下我在北京看到的风景名胜。

Beijing is China's capital. I visited Beijing three times, in 2010, 2011, and 2013. I'd like to revisit my sightseeing trips to Beijing in first "virtual travel" of 2021.

运动员去过的地方 | Where the Athletes Have Been

2008年，北京举办了夏季奥林匹克运动会，其中主要的两个体育场馆“鸟巢”、“水立方”特别令人瞩目。 2010年8月7日，“大约”是奥运会开幕两周年，我来到北京奥林匹克公园参观鸟巢、水立方。

Beijing is the host city of 2008 Summer Olympics. The most notable place of 2008 Olympics was "Bird Nest" and "Water Cube". On August 7, 2010, approximately two years since the opening ceremony of 2008 Olympics, I came to Beijing Olympic Green to visit these two venues.

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What is a "Face" in Named Data Networking?

Junxiao Shi
last updated

Face is an overloaded term in Named Data Networking (NDN). Most developers have some feeling of what a face is, but often find it hard to explain. This article attempts to demystify the concept of face in NDN.

"Face" as Defined in Publications

The original NDN paper, Networking Named Content, introduces the term face in a footnote:

We use the term face rather than interface because packets are not only forwarded over hardware network interfaces but also exchanged directly with application processes within a machine.

NFD, the original NDN forwarder software, explains in the NFD Developer Guide:

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The Reality of NDN Video Streaming

Junxiao Shi

As of 2019, video accounts for over 60% of downstream traffic on the Internet. It is believed that video streaming could benefit from the in-network caching feature of Named Data Networking (NDN), which would reduce the total traffic volume and bring cost savings for Internet service providers and content publishers. Far Cry: Will CDNs Hear NDN's Call?, a paper published at ACM-ICN 2020 conference, is the latest attempt on NDN video streaming.

How iViSA Works

In Far Cry, the authors implemented iViSA, a browser-based video streaming application that runs on the global NDN testbed, and then performed some comparison study between this application and similar HTTP video streaming application deployed on commercial CDN services.

It's said that if you want reproducible science, the software needs to be open source. The authors released most of their source code, and we can get a peek into how iViSA actually works.

The backend server repository contains:

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NFD nightly went APT

Junxiao Shi

NOTICE Instructions in this article are outdated. Please see latest information in NFD nightly usage.

Last year, I started building NFD nightly packages in GitHub Actions. So far, installation is a manual procedure: the user must manually download the ZIP files from nfd-nightly.ndn.today, decompress them, and figure out the dependency among various .deb packages. Starting today, I'm publishing NFD nightly packages in an APT repository, and you can install them with apt-get command.

Add the NFD nightly APT repository

Add the repository with the command that matches your platform:

# Ubuntu 18.04 (bionic), amd64 (laptops and servers)
echo "deb [trusted=yes] https://nfd-nightly-apt.ndn.today/ubuntu bionic main" \
  | sudo tee /etc/apt/sources.list.d/nfd-nightly.list

# Ubuntu 20.04 (focal), amd64 (laptops and servers)
echo "deb [trusted=yes] https://nfd-nightly-apt.ndn.today/ubuntu focal main" \
  | sudo tee /etc/apt/sources.list.d/nfd-nightly.list

# Debian 10 (buster), amd64 (laptops and servers)
echo "deb [trusted=yes] https://nfd-nightly-apt.ndn.today/debian buster main" \
  | sudo tee /etc/apt/sources.list.d/nfd-nightly.list

# Debian 10 (buster), armv7 (Raspberry Pi 3 or 4)
echo "deb [trusted=yes] https://nfd-nightly-apt.ndn.today/debian buster main" \
  | sudo tee /etc/apt/sources.list.d/nfd-nightly.list

# Debian 10 (buster), armv6 (Raspberry Pi Zero W)
echo "deb [trusted=yes] https://nfd-nightly-apt.ndn.today/raspberrypi buster main" \
  | sudo tee /etc/apt/sources.list.d/nfd-nightly.list
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