Added new post about inotify leaking in kubelet

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-url     : "https://blog.pengzhan.dev"  # "https://dev.pengzhan.dev"
+url     : "https://dev.pengzhan.dev"
 baseurl : ""
-fakebaseurl: "" # "/proxy/4000"
+fakebaseurl: "/proxy/4000"
 title   : "STSD"
 description: > # this means to ignore newlines until "Language & timezone"
     My personal blog, some contents are useful, the others are not. Just like my mediocre life.

_posts/2024-04-11-Debug-kubelet.md

@@ -27,4 +27,4 @@ TL;DR: Bumping up to level 5 would satisfy most debugging needs.
 By the time, this note was written. In `kubelet` related code, level 8 was only used in `pkg/kubelet/prober/prober_manager.go` and level 7 was only used in `pkg/kubelet/logs/container_log_manager.go`.  And there are  11 occurrences that level 6 was used, and all of them are not part of workload lifecycle related.
 
 ## Further readings
-[Inotify watcher leaks in Kubelet]
+[Inotify watcher leaks in Kubelet](/posts/inotify-watcher-leaks-in-kubelet.html)

_posts/2024-04-11-inotify-watcher-leaks-in-kubelet.md

@@ -1,12 +1,156 @@
 ---
-layout: post
 title: Inotify watcher leaks in Kubelet
-date: 2024-04-11 16:35 -0400
+date: 2024-04-18 16:35 -0400
 description: 
-cover: 
+cover: '/static/2024-04/kubelet_inotify_leak_logo.png'
 category: 
-tags: 
-published: false
+tags: ["Kubernetes", "Kubelet", "Debug", "Inotify"]
+published: true
 sitemap: true
 permalink: 
+author: Pengzhan Hao
 ---
+
+## Symptom
+Recently, I faced an issue where Kubelet on a node reported error message failed to create file descriptors.
+
+```bash
+error creating file watcher: too many open files
+error creating file watcher: no space left on device
+```
+
+After short checking, I found the node has `max_user_watches` of 10000, but the `TotalinotifyWatches` is beyond this value. (P. S still not sure why watcher can initiate more than cap). In order to find which process occupied the most watchers. I used following command[^flbit_ino] to find it out.
+
+```bash
+echo -e "COUNT\tPID\tUSER\tCOMMAND"; sudo find /proc/[0-9]*/fdinfo -type f 2>/dev/null | sudo xargs grep ^inotify 2>/dev/null | cut -d/ -f 3 | uniq -c | sort -nr | { while read -rs COUNT PID; do echo -en "$COUNT\t$PID\t"; ps -p $PID -o user=,command=; done}
+
+COUNT	PID	USER	COMMAND
+7491	8412	root /home/kubernetes/bin/kubelet --v=2 --cloud-provide=gce --experi
+2620	1	root /sbin/init
+....
+```
+
+Surprisingly, Kubelet initiated more than 7000 inotify watchers. I assumed there was an inotify leakage in Kubelet.
+## Leakage check
+
+### Clean Kubelet
+To better understand the situation, I created a clean cluster with only 1 clean node on GKE. Roughly 70 inotify watchers were there. I created a single nginx pod and the number increased by 3. Theoretically, these 3 watchers are used by Kubelet to monitor any changes on `rootfs `, `kube-api-access` and `PodSandbox`. But to verify it, we need to check more details on which inodes are monitored by Kubelet. 
+### Check inotify file descriptors
+To do so, let's take a look how to track a single inotify file descriptor. Opened processes' `fdinfo` folder, we can examine each or them to find an inotify fd. 
+
+```bash
+# Find kubelet pid
+ps -aux | grep kubelet
+KPID=2430
+
+# File the an example fd
+sudo ls /proc/2430/fdinfo
+
+0 1 10 11 12 13 14 2 3 4 5 6 7 8 9
+
+...
+
+sudo cat /proc/2430/fdinfo/8
+
+pos:	0
+flags:	02004000
+mnt_id:	15
+ino:	1057
+inotify wd:1 ino:3f327 sdev:800001 mask:fc6 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27f30300e5059ea2
+```
+
+This is very confusing, so I rely on `man proc`[^man_proc] to understand every piece of them. In given fd, the needed information to continue sit in the last line. It's an inotify entry represents the 1 file or folder to be monitored. And the most useful data is `ino:3f327` which represents the inode number of target file (in hexadecimal). And `sdev:800001`, which represents the ID of device where the inode sit on, and it's also in hex.
+
+Using `lsblk`, I can see there's only 1 disk I'm using on the node, so finding the target file would be easy.
+
+```bash
+# Cast to decimal
+ino=3f327
+dec="$((16#${ino}))"
+
+# Find the target file
+loc="debugfs -R 'ncheck ${dec}' /dev/sda1"
+sudo eval $loc 2>/dev/null
+
+debugfd 1.46.5 (30-Dec-2021)
+Inode	Pathname
+258855	/etc/srv/kubernetes/pki/ca-certificates.crt
+```
+
+Put all processes above into one single script, I can retrieve all target files, that would help to understand if there's a real leakage. Also, I count the unique inode amount, this could also help to know which inode are monitored multiple times.
+
+```bash
+cat << EOF | sudo tee -a test.sh
+echo "kubelet pid="${PID}
+in_fds=$(find /proc/${PID}/fdinfo -type f 2>/dev/null | xargs grep ^inotify | cut -d " " -f 3 | cut -d ":" -f 2)
+echo ${in_fds}
+echo "Count: $(find /proc/${PID}/fdinfo -type f 2>/dev/null | xargs grep ^inotify | wc -l)"
+
+uniq_fds=$(echo "${in_fds[@]}" | sort | uniq)
+echo ${uniq_fds}
+
+while read -r element;
+do
+  count=$(echo "${in_fds[@]}" | grep -o "${element}" | wc -l)
+  dec="$((16#${element}))"
+  loc="debugfs -R 'ncheck ${dec}' /dev/sda1"
+  loc=$(eval $loc 2>/dev/null | tail -1 | cut -d " " -f 4)
+  printf "%-6s %-10s %-6s %s\n" "${element}" "${dec}" "${count}" "${loc}"
+done <<< "${uniq_fds}"
+EOF
+
+sudo bash test.sh
+
+kubelet pid=2430
+3f327 3f321 ...
+Count: 120
+1 10b 1259 128a ...
+1	1	72	Inode	Pathname
+10b	267	1	267	/etc/systemd/system/multi-user.target.wants/snapd.service
+...
+```
+
+The given results are consists by following parts:
+- One line for get Kubelet pid
+- One line for all target inode numbers
+- One line for tell how many unique inode (120)
+- One line of sorted target
+- Following 120 lines, each of them represents a unique inode number, its decimal number, count, another time of decimal number and the target file path.
+
+I used the same script to the problematic node, and it showed the following result. In summary, most Kubelet watchers were targeting `ino:1 `. And there are 6649 targets files, which likely to be leakage, because there were only 150 pods on this pod. Unfortunately, `debugfs` can't find any target files, so the output showed as meaningless string `"Inode Pathname"`.
+
+```
+kubelet pid=8412
+...
+Count: 7491
+...
+1	1	6649	Inode Pathname
+```
+
+### Bad apple
+Why `debugfs` can't help anymore? The reason is simple, each cgroup for a pod is using its own rootfs. This means the watcher are somehow residing on different rootfs and using independent inode index.  There are some other ways to do it, I choose the most common tool `grep` to find out.
+
+```
+sudo grep / -inum 1
+/home/kubernetes/containerized_mounter/rootfs/dev
+/home/kubernetes/containerized_mounter/rootfs/proc
+...
+/home/kubernetes/containerized_mounter/rootfs/var/lib/kubelet/pods/5325873d-f2a0-48df-83e2-0b911df2f77f/volumes/kubernetes.io~projected/kube-api-access-227jg
+...
+/dev
+/boot/efi
+...
+```
+
+This turns things easy, because I can just use pod ID to compare between running pods to find out if there are any terminated pods are there. And it did show there's some non-existence pods still being watched somehow.
+
+## What to expect next
+
+- [How Kubelet leaked inotify watchers?]()
+- [debugfs]()
+
+## References
+
+[^flbit_ino]: [Fluentbit error "cannot adjust chunk size" on GKE](https://stackoverflow.com/a/76712244)
+[^man_proc]: [proc(5)](https://manpages.courier-mta.org/htmlman5/proc.5.html)
+[^list_ino]: [Listing the files that are being watched by `inotify` instances](https://unix.stackexchange.com/a/646113)