wip: writing documentation

docker/alpine/gettting-started.md

@@ -17,9 +17,15 @@ for further details about `wmpidproxy`.
 It also useful for setting the process as process group leader.
 Read [here](#wingmate-exec-binary) for further details about `wmexec`.
 
-## Building your image based on wingmate image in Docker Hub
+## Building a container image based on wingmate image in Docker Hub
+
+Wingmate has no dependency other than `alpine` base image, so you just need to copy
+the binaries directly. If you have built your application into an `alpine` based image,
+all you need to do is copy whichever binary you need, crontab file (if you use cron)
+and add some shell script to glue them together. Here is a Dockerfile example.
 
 ```Dockerfile
+# Dockerfile
 FROM suyono/wingmate:alpine as source
 
 FROM alpine:latest
@@ -31,10 +37,15 @@ COPY --from=source /usr/local/bin/wmexec /usr/local/bin/wmexec
 ENTRYPOINT [ "/usr/local/bin/entry.sh" ]
 CMD [ "/usr/local/bin/wingmate" ]
 ```
-
+You can find some examples for shell script in this [directory](../alpine/).
 
 ## Configuration
 
+When `wingmate` binary starts, it will look for some files. By default, it will
+try to read the content of `/etc/wingmate` directory. You can change the directory
+where it reads by setting `WINGMATE_CONFIG_PATH` environment variable. The structure
+inside the config path should look like this.
+
 ```shell
 /etc
  └── wingmate
@@ -48,7 +59,32 @@ CMD [ "/usr/local/bin/wingmate" ]
          └── spawner.sh
 ```
 
-## Appendix
-### Wingmate core binary
-### Wingmate PID Proxy binary
-### Wingmate Exec binary
+First, `wingmate` will try to read the content of `service` directory. The content of
+this directory should be executables (either shell scripts or binaries). The wingmate
+will run every executable in `service` directory without going into any subdirectory.
+
+Next, `wingmate` will read the `crontab` file. `wingmate` expects the `crontab` file using
+common UNIX crontab file format. Something like this
+
+```shell
+ ┌───────────── minute (0–59)
+ │ ┌───────────── hour (0–23)
+ │ │ ┌───────────── day of the month (1–31)
+ │ │ │ ┌───────────── month (1–12)
+ │ │ │ │ ┌───────────── day of the week (0–6) (Sunday to Saturday)
+ │ │ │ │ │ 
+ │ │ │ │ │
+ │ │ │ │ │
+ * * * * * <commad or shell script or binary>
+```
+
+The command part only support simple command and arguments. Shell expression is not supported
+yet. It is recommended to write a shell script and put the path to shell script in
+the command part.
+
+# Appendix
+## Wingmate core binary
+### Service
+### Cron
+## Wingmate PID Proxy binary
+## Wingmate Exec binary