feat: flip swap mechanism on sagitta — MD as primary, RST as override

Mirror of #1899 (current) and #1900 (circinus) for sagitta. Same logic,
same scripts, per-branch file set.

Changes:
- Rename docs/**/md-<stem>.md to docs/**/<stem>.md (drop md- prefix) for
  all 210 stems previously listed in docs/_swap.txt
- Rename docs/**/<stem>.rst to docs/**/rst-<stem>.rst (add rst- prefix)
  for the same 210 stems
- Repurpose docs/_swap.txt as docs/_rst_overrides.txt; initially empty
- conf.py exclude_patterns flipped: rst-*.rst excluded by default
- conf.py runtime-artifact references updated to _rst_override_state.json
  and _md_exclude.txt
- scripts/swap_sources.py imported from current (post-#1899 rewrite, with
  inverted rename direction)
- scripts/import_myst.py and tests/test_import_myst.py deleted (obsolete)
- tests/test_swap_sources.py imported from current (post-#1899 rewrite)

Side-effect: fixes the same 404 on /en/1.4/ View page source links that
#1899 fixed for /en/rolling/ and #1900 fixed for /en/1.5/.

Per-branch differences vs #1899:
- sagitta has 210 stems vs current's 254 (sagitta has no vpp pages and
  fewer current-only features; cli + installation/cloud/aws are still
  RST-only on sagitta pending the title-level fix follow-up)
- otherwise the script/conf.py/test changes are byte-identical with current

Generated by robots https://vyos.io

1 files changed, 191 insertions, 0 deletions

diff --git a/docs/contributing/debugging.md b/docs/contributing/debugging.md
new file mode 100644
index 00000000..73b622c6
--- /dev/null
+++ b/docs/contributing/debugging.md
@@ -0,0 +1,191 @@
+(debugging)=
+
+# Debugging
+
+There are two flags available to aid in debugging configuration scripts.
+Since configuration loading issues will manifest during boot, the flags are
+passed as kernel boot parameters.
+
+## ISO image build
+
+When having trouble compiling your own ISO image or debugging Jenkins issues
+you can follow the steps at {ref}`iso_build_issues`.
+
+## System Startup
+
+The system startup can be debugged (like loading in the configuration
+file from `/config/config.boot`. This can be achieve by extending the
+Kernel command-line in the bootloader.
+
+### Kernel
+
+- `vyos-debug` - Adding the parameter to the linux boot line will produce
+  timing results for the execution of scripts during commit. If one is seeing
+  an unexpected delay during manual or boot commit, this may be useful in
+  identifying bottlenecks. The internal flag is `VYOS_DEBUG`, and is found
+  in [vyatta-cfg]. Output is directed to `/var/log/vyatta/cfg-stdout.log`.
+- `vyos-config-debug` - During development, coding errors can lead to a
+  commit failure on boot, possibly resulting in a failed initialization of the
+  CLI. In this circumstance, the kernel boot parameter `vyos-config-debug`
+  will ensure access to the system as user `vyos`, and will log a Python
+  stack trace to the file `/tmp/boot-config-trace`.
+  File `boot-config-trace` will generate only if config loaded with a failure
+  status.
+
+## Live System
+
+A number of flags can be set up to change the behaviour of VyOS at runtime.
+These flags can be toggled using either environment variables or creating
+files.
+
+For each feature, a file called `vyos.feature.debug` can be created to
+toggle the feature on. If a parameter is required it can be placed inside
+the file as its first line.
+
+The file can be placed in `/tmp` for one time debugging (as the file
+will be removed on reboot) or placed in '/config' to stay permanently.
+
+For example, `/tmp/vyos.ifconfig.debug` can be created to enable
+interface debugging.
+
+It is also possible to set up the debugging using environment variables.
+In that case, the name will be (in uppercase) VYOS_FEATURE_DEBUG.
+
+For example running, `export VYOS_IFCONFIG_DEBUG=""` on your vbash,
+will have the same effect as `touch /tmp/vyos.ifconfig.debug`.
+
+- `ifconfig` - Once set, all commands used, and their responses received
+  from the OS, will be presented on the screen for inspection.
+- `command` - Once set, all commands used, and their responses received
+  from the OS, will be presented on the screen for inspection.
+- `developer` - Should a command fail, instead of printing a message to the
+  user explaining how to report issues, the python interpreter will start a
+  PBD post-mortem session to allow the developer to debug the issue. As the
+  debugger will wait from input from the developer, it has the capacity to
+  prevent a router to boot and therefore should only be permanently set up
+  on production if you are ready to see the OS fail to boot.
+- `log` - In some rare cases, it may be useful to see what the OS is doing,
+  including during boot. This option sends all commands used by VyOS to a
+  file. The default file is `/tmp/full-log` but it can be changed.
+
+:::{note}
+In order to retrieve the debug output on the command-line you need to
+disable `vyos-configd` in addition. This can be run either one-time by
+calling `sudo systemctl stop vyos-configd` or make this reboot-safe by
+calling `sudo systemctl disable vyos-configd`.
+:::
+
+### FRR
+
+Recent versions use the `vyos.frr` framework. The Python class is located
+inside our `vyos-1x:python/vyos/frr.py`. It comes with an embedded debugging/
+(print style) debugger as vyos.ifconfig does.
+
+To enable debugging just run: `$ touch /tmp/vyos.frr.debug`
+
+### Debugging Python Code with PDB
+
+Sometimes it might be useful to debug Python code interactively on the live
+system rather than a IDE. This can be achieved using pdb.
+
+Let us assume you want to debug a Python script that is called by an op-mode
+command. After you found the script by looking up the op-mode-defitions you
+can edit the script in the live system using e.g. vi:
+`vi /usr/libexec/vyos/op_mode/show_xyz.py`
+
+Insert the following statement right before the section where you want to
+investigate a problem (e.g. a statement you see in a backtrace):
+`import pdb; pdb.set_trace()`
+Optionally you can surrounded this statement by an `if` which only triggers
+under the condition you are interested in.
+
+Once you run `show xyz` and your condition is triggered you should be dropped
+into the python debugger:
+
+```none
+> /usr/libexec/vyos/op_mode/show_nat_translations.py(109)process()
+-> rule_type = rule.get('type', '')
+(Pdb)
+```
+
+You can type `help` to get an overview of the available commands, and
+`help command` to get more information on each command.
+
+Useful commands are:
+
+- examine variables using `pp(var)`
+- continue execution using `cont`
+- get a backtrace using `bt`
+
+### Config Migration Scripts
+
+When writing a new configuration migrator it may happen that you see an error
+when you try to invoke it manually on a development system. This error will
+look like:
+
+```none
+vyos@vyos:~$ /opt/vyatta/etc/config-migrate/migrate/ssh/0-to-1 /tmp/config.boot
+Traceback (most recent call last):
+  File "/opt/vyatta/etc/config-migrate/migrate/ssh/0-to-1", line 31, in <module>
+    config = ConfigTree(config_file)
+  File "/usr/lib/python3/dist-packages/vyos/configtree.py", line 134, in __init__
+    raise ValueError("Failed to parse config: {0}".format(msg))
+ValueError: Failed to parse config: Syntax error on line 240, character 1: Invalid syntax.
+```
+
+The reason is that the configuration migration backend is rewritten and uses
+a new form of "magic string" which is applied on demand when real config
+migration is run on boot. When running individual migrators for testing,
+you need to convert the "magic string" on your own by:
+
+```none
+vyos@vyos:~$ /usr/libexec/vyos/run-config-migration.py --virtual --set-vintage vyos /tmp/config.boot
+```
+
+### Configuration Error on System Boot
+
+Being brave and running the latest rolling releases will sometimes trigger
+bugs due to corner cases we missed in our design. Those bugs should be filed
+via [Phabricator] but you can help us to narrow down the issue. Login to your
+VyOS system and change into configuration mode by typing `configure`. Now
+re-load your boot configuration by simply typing `load` followed by return.
+
+You should now see a Python backtrace which will help us to handle the issue,
+please attach it to the [Phabricator] task.
+
+### Boot Timing
+
+During the migration and extensive rewrite of functionality from Perl into
+Python a significant increase in the overall system boottime was noticed. The
+system boot time can be analysed and a graph can be generated in the end which
+shows in detail who called whom during the system startup phase.
+
+This is done by utilizing the `systemd-bootchart` package which is now
+installed by default on the VyOS 1.3 (equuleus) branch. The configuration is
+also versioned so we get comparable results. `systemd-bootchart` is configured
+using this file: [bootchart.conf]
+
+To enable boot time graphing change the Kernel commandline and add the following
+string: `init=/usr/lib/systemd/systemd-bootchart`
+
+This can also be done permanently by changing `/boot/grub/grub.cfg`.
+
+## Priorities
+
+VyOS CLI is all about priorities. Every CLI node has a corresponding
+`node.def` file and possibly an attached script that is executed when the
+node is present. Nodes can have a priority, and on system bootup - or any
+other `commit` to the config all scripts are executed from lowest to highest
+priority. This is good as this gives a deterministic behavior.
+
+To debug issues in priorities or to see what's going on in the background
+you can use the `/opt/vyatta/sbin/priority.pl` script which lists to you
+the execution order of the scripts.
+
+
+```{include} /_include/common-references.txt
+```
+
+
+[bootchart.conf]: https://github.com/vyos/vyos-build/blob/current/data/live-build-config/includes.chroot/etc/systemd/bootchart.conf
+[vyatta-cfg]: https://github.com/vyos/vyatta-cfg