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https://github.com/jlevy/procdog

Lightweight command-line process control
https://github.com/jlevy/procdog

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Lightweight command-line process control

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# procdog



## Lightweight command-line process control



Procdog (as in "**proc**ess watch**dog**"... get it?)

is a simple command-line tool to start, stop, and check the health of

processes. It works with any kind of process you can invoke from the command

line (be it native, Java, Node, Python, or anything) on MacOS or Linux.



Why would you want another tool for this?



- For basic interactive situations, you can just run a process in a terminal

  or use job management in your shell (`jobs`, `kill`, etc.).

- But you rapidly realize this won't work well once you have longer-lived processes

  or are `ssh`ing to remote servers. Then you could use `nohup` and manually

  checking with `ps`, or using [screen](http://en.wikipedia.org/wiki/GNU_Screen).

  But these don't script easily.

- You also might want to script starting and stopping.

  With a little effort you might write a custom Bash script (writing a PID file,

  using `pgrep` and `pkill`, etc.), but it's a hassle and gets messy quickly.

- Of course, you can just "do it right." Traditionally, in the Unix world, the way to

  control services are

  [System V service scripts](http://manpages.ubuntu.com/manpages/trusty/man8/service.8.html),

  [start-stop-daemon](http://manpages.ubuntu.com/manpages/karmic/man8/start-stop-daemon.8.html),

  [Upstart](http://upstart.ubuntu.com/), or

  [systemd](http://www.freedesktop.org/wiki/Software/systemd/).

  Using these is essential for production deployment, but they tend to be a bit arcane

  and highly OS-dependent, so aren't as convenient for casual use, and you can't easily

  develop and test on both MacOS and Linux (as many of us try to do).



Procdog is an alternative for developers that attempts to be easy to install,

simple and obvious to use, and cross-platform. Processes are independent of the

shell used to invoke them (i.e., detatched as with `nohup`) and you can also check

status or kill them at any time (as with a Unix service).



Probably the most simlar tool to Procdog is [Supervisor](https://github.com/Supervisor/supervisor).

Although it has similar goals, Supervisor is a more complex, production-oriented tool with a

long-lived, centrailized XML-RPC server that monitors processes. Procdog is intended

to be a single, simple, easy-to-use command that needn't be set up and managed itself

or run as root. Each use of Procdog is independent and monitors just one process. It

does not require a configuration file unless you want to save typing. You can even

check the Procdog script into your own project so developers can immediately use it

locally, since it has no dependencies (besides Python 2.7).



You'll find it useful if you have servers, databases, or other processes you want

to manage on your personal machine when developing, in build systems and test

harnesses, test deployments, etc. Currently, it *doesn't* have restart

logic, log file rotation, or some other features you may want for a production

environments; for this consider Supervisor, Upstart, systemd, & co. Procdog is

also *way* less mature than these alternatives.



## Installation



No dependencies except Python 2.7+. It's easiest to install with pip:



    sudo pip install procdog



Or, since it's just one file, you can copy the single

[`procdog`](https://github.com/jlevy/procdog/blob/master/procdog)

script somewhere (perhaps within your own project) and make it executable.



## Quick start



Now you can start and monitor any process (here let's pick "sleep" -- not all that

useful, but you already have it):



```

$ procdog start myprocess --command "sleep 100"

running, pid=14969

$ procdog status myprocess

running, pid=14969

$ procdog stop myprocess

stopped

$

```



Note you have to give your process an arbitrary name (`myprocess` here), like a Unix

service name, so you can refer to it. Once the process is done, the monitor daemon

also exits.



## Usage



Run `procdog -h` for help on all options.



## A better example



Now, with a real server we'd like to know if it's actually up and doing something,

like listening on a port. Procdog supports an arbitrary command to test health

(e.g. running `curl` to see if it returns a result) and can wait until a server

is running and tell you.



```

$ procdog start backend --command="java -classpath my-backend.jar com.example.BackendServer server config.yml" \

  --health-command="curl http://localhost:8080/ping" \

  --health-count=10 --health-delay=2 \

  --dir=$HOME/backend \

  --stdout=backend.log --stderr=backend.log --append \

  --ensure-healthy --strict

running, health=0, pid=15240

$ procdog status backend

running, health=0, pid=15240

$ procdog stop backend --strict

stopped

$ procdog stop backend --strict

procdog: error: process 'backend' is not running

$

```



Some notes on this:



- We can specify where to write stdout and stderr. They can be the same or different.

  Existing log files are appended to if you use `--append`.

- The health command simply calls a shell command to see if the server is healthy.

  The return code of the health check command must be `0` for the server to be considered

  healthy. In this case, we're callin `curl` on a known health-check URL, which will have

  return code 0 on an HTTP 200

- The `--ensure-healthy` option means the command will block until the process is healthy,

  or until the daemon gives up and kills the process (if necessary). In this example,

  it will try 10 times, sleeping 2 seconds each time, before giving up.

- The `--dir` option means process will run from that directory.

- We ask the client to be `--strict`, so that it returns non-zero status code when we try to

  start a process that's already running or or stop one that is already stopped.



## Configuration files



It's possible to avoid typing by putting most options in a configuration file:



```

# Procdog config file. Each section is a process name.

[backend]

command=java -classpath my-backend.jar com.example.BackendServer server config.yml

health_command=curl http://localhost:8080/ping

health_count=10

health_delay=2.

dir=$HOME/backend

stdout=backend.log

stderr=backend.log

append=False

ensure_healthy=True

strict=True

```



You have any number of sections, one section per process. Procdog reads options

from `~/.procdog.cfg` or `procdog.cfg` (in the same directory the `procdog`

script resides). Any options given on the command line override those in the

configuration file. Note that environment variables (like `$HOME`) are

allowed and expanded. Once you have the above section in your config file,

you can run:



```

$ procdog start backend

running, health=0, pid=15396

$ procdog stop backend

stopped

$

```



## How it works



Procdog starts a small daemon that `popen()`s and monitors the process.

The daemon listens and accepts commands on a local

[Unix domain socket](http://en.wikipedia.org/wiki/Unix_domain_socket),

making it possible to check the process is running or terminate it, and to do simple

health checks. You can see these sockets at `/var/tmp/procdog.*.sock` (where the * is the

id of the process). For simplicity, there is a single Procdog daemon for each monitored

process, so each process is handled compeltely separately.



We use Unix domain sockets so that we don't have the headaches of pid files or

choosing and binding to TCP ports. They're also available on most platforms.



Daemon logs are sent to `/var/tmp/procdog.*.log`. Usually you'll want to redirect your

process stdout and stderr using the `--stdout` and `--stderr` options.



Procdog is quite new so probably not stable. Bug reports and contributions are welcome!



## Tests



All basic features are covered with a simple Bash-based regression test.



To run it, clone this repo, invoke `tests/run.sh` then follow the directions to diff

the output using `git`.



## License



[Apache 2](https://github.com/jlevy/procdog/blob/master/LICENSE).