Add article about cdist/openwrt

content/u/blog/2024-08-02-openwrt-no-cdist-yet/contents.lr

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+title: cdist does not (yet) fully support OpenWrt
+---
+pub_date: 2024-08-02
+---
+author: ungleich networking team
+---
+twitter_handle: ungleich
+---
+_hidden: no
+---
+_discoverable: yes
+---
+abstract:
+How we try to use cdist on openwrt and fail
+---
+body:
+
+## cdist config management
+
+As many of you know, we use
+[cdist](https://cdi.st) for configuration management at ungleich. And
+we try to manage everything that is not (yet) in kubernetes with it.
+
+Today's short blog entry is about using cdist with openwrt.
+
+## OpenWrt at ungleich
+
+[OpenWrt](https://openwrt.org] is a popular, open source operating
+system used on routers, switches, etc. We use it for providing IPv6
+and IPv4 connectivity to customers world wide.
+
+So far most of our devices are configured using shell scripts from our
+[ungleich-tool git
+repository](https://code.ungleich.ch/ungleich-public/ungleich-tools).
+
+However as configurations get more complex, we thought about moving
+our configuration also into cdist.
+
+## OpenWrt is similar, but not the same
+
+OpenWrt is, generally speaking, "just another Linux distribution",
+albeit with a very, very small footprint. It has to be, because the
+storage on a typical router can be in the size of a couple Megabytes.
+Right, not Gigabyte, not Terabyte.
+
+For instance this "large" router has about 9 Megabytes of storage:
+
+```
+# df -h
+Filesystem                Size      Used Available Use% Mounted on
+/dev/root                 4.0M      4.0M         0 100% /rom
+tmpfs                   217.0M    240.0K    216.8M   0% /tmp
+/dev/mtdblock6            9.1M    420.0K      8.7M   4% /overlay
+overlayfs:/overlay        9.1M    420.0K      8.7M   4% /
+tmpfs                   512.0K         0    512.0K   0% /dev
+```
+
+It does however have 512 MiB of RAM...:
+
+```
+# free -m
+              total        used        free      shared  buff/cache   available
+Mem:         444428       57120      370184         240       17124      354048
+Swap:             0           0           0
+```
+
+So, openwrt is a Linux distribution, but its environment is a bit more
+challenging than a general purpose Linux distribution.
+
+## cdist & openwrt
+
+Cdist uses so called "types" to configure systems idempotently. They
+usually require some shell support on the target system, but nothing
+fancy.
+
+However in the case of openwrt, cdist is missing some support, as of
+version 7.0.0:
+
+* cdist uses the system default ssh and if that uses SFTP instead of
+  SCP by default, it will fail, as openwrt, as of 23.05.3, only
+  supports legacy scp (-O). Manually patching cdist source code to
+  include "-O" fixes this issue for the moment.
+
+* the most basic cdist type __file uses "cksum" to create a checksum
+  over files to decide whether or not to copy a file. cksum was chosen
+  in the first place, as it is very basic and can be found
+  everywhere. Well, everywhere but on openwrt...
+
+
+## Future of cdist & openwrt
+
+Both above issues can in theory be addressed, but the __file type is
+very basic and needs some checksumming support. Without it, cdist
+lacks a major feature and can be considered not (yet) usable.
+
+Let's see what the future brings.