# Config Management, part II: Microcode Language


[The first part](/2024/january/29/config-management/).

This cfg mgmt system uses a micro language to perform the changes on the target
system. This language is limited in its scope and has the following "instructions":

INSTRUCTION | ARITY | ARGUMENTS | REMARK
------------|-------|-----------|-----
 REM        | 1     | TEXT | a comment
 MKDIR      | 2     | MODE PATH | create a directory
 COPY       | 2     | SRC-PATH DST-PATH | copy a file
 CHMOD      | 2     | MODE PATH | set the mode
 CHOWN      | 2     | USER/ID PATH | set the owner
 CHGRP      | 2     | GROUP/ID PATH | set the group
 RM         | 1     | PATH | rm the file
 EXEC       | 1     | CMD | install a package

These micro-instruction basically all call a simple system call to make the changes.
Note, except for the latter this is the Unix API of everything is a file. `EXEC` is now only used
to install/deinstall a package; of course such a generic instruction is ripe for abuse...

Each of these instructions has an (implicit?) condition attached. For example COPY will
only copy a file if the destination differs from the source in some way.

Instructions always have an action attached to them, so if the condition is false, the instruction
executes and the resulting action is also performed. The actions I can think of are:

ACTION | ARITY | ARGUMENTS | REMARK
-------|-------|-----------|-------
NOP    |   0   |           | do nothing
SYSCTL |   2   | COMMAND UNIT | execute systemctl

Using an example, some snippet of a higher level language generated
the following microcode, the condition is implicit, the action is after the `&&`:

    REM file blah generated this
    EXEC   apt-get install coredns            && NOP
    COPY   Corefile /etc/coredns/Corefile     && SYSCTL restart-or-reload coredns
    CHOWN  coredns /etc/coredns/Corefile      && SYSCTL restart-or-reload coredns
    CHGRP  coredns /etc/coredns/Corefile      && SYSCTL restart-or-reload coredns
    COPY   db.example /etc/coredns/db.example && SYSCTL restart-or-reload coredns
    CHOWN  coredns /etc/coredns/db.example    && SYSCTL restart-or-reload coredns
    CHGRP  coredns /etc/coredns/db.example    && SYSCTL restart-or-reload coredns

Now when we run through this we just do what it says (we can defer the SYSCTLs and only do them
once).

In its core this system will parse a text file with micro-instruction and execute them. There is
some intelligence needed to be efficient and do as little work as possible, but we can brush that
aside as optimization (for now).

I also really like this file to be in plain text, you can even edit it! And note there is also
an implicit version (git hash) to facilitate rollback (and roll forwards). See the first part for
some incoherent thoughts on that.