entrypoint/: run given command

refs #2

deps.Dockerfile

@@ -1,3 +1,11 @@
+FROM golang:buster as entrypoint
+
+COPY entrypoint /entrypoint
+
+WORKDIR /entrypoint
+RUN ["go", "build", "."]
+
+
 FROM debian:buster-slim
 
 RUN ["bash", "-exo", "pipefail", "-c", "export DEBIAN_FRONTEND=noninteractive; apt-get update; apt-get install --no-install-{recommends,suggests} -y locales; apt-get clean; rm -vrf /var/lib/apt/lists/*"]
@@ -6,6 +14,8 @@ RUN ["locale-gen", "-j", "4"]
 
 RUN ["bash", "-exo", "pipefail", "-c", "export DEBIAN_FRONTEND=noninteractive; apt-get update; apt-get install --no-install-{recommends,suggests} -y apache2 libapache2-mod-php7.3 php-{imagick,redis} php7.3-{bcmath,bz2,common,curl,dba,enchant,gd,gmp,imap,interbase,intl,json,ldap,mbstring,mysql,odbc,opcache,pgsql,pspell,readline,recode,snmp,soap,sqlite3,sybase,tidy,xml,xmlrpc,xsl,zip}; apt-get clean; rm -vrf /var/lib/apt/lists/*"]
 
+COPY --from=entrypoint /entrypoint/entrypoint /entrypoint
+
 RUN ["a2enmod", "rewrite"]
 RUN ["ln", "-vsf", "/dev/stdout", "/var/log/apache2/access.log"]
 RUN ["ln", "-vsf", "/dev/stderr", "/var/log/apache2/error.log"]
@@ -18,3 +28,5 @@ EXPOSE 8080
 RUN ["chmod", "o+x", "/var/log/apache2"]
 RUN ["chown", "www-data:www-data", "/var/run/apache2"]
 RUN ["install", "-o", "www-data", "-g", "www-data", "-d", "/etc/icingaweb2"]
+
+ENTRYPOINT ["/entrypoint"]

entrypoint/go.mod

@@ -0,0 +1,3 @@
+module entrypoint
+
+go 1.14

entrypoint/main.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"syscall"
+	"time"
+)
+
+func main() {
+	if err := entrypoint(); err != nil {
+		logf("crit", "%s", err.Error())
+		os.Exit(1)
+	}
+}
+
+func entrypoint() error {
+	if len(os.Args) < 2 {
+		logf("warn", "Nothing to do.")
+		return nil
+	}
+
+	path := os.Args[1]
+	if filepath.Base(path) == path {
+		logf("info", "Looking up %#v in $PATH", path)
+
+		abs, errLP := exec.LookPath(path)
+		if errLP != nil {
+			return errLP
+		}
+
+		path = abs
+	}
+
+	logf("info", "Running %#v", path)
+	return syscall.Exec(path, os.Args[1:], os.Environ())
+}
+
+var out = bufio.NewWriter(os.Stderr)
+
+func logf(severity, format string, a ...interface{}) {
+	_, _ = fmt.Fprintf(out, "[%s] ", time.Now().Format("Mon Jan 2 15:04:05.999999999 2006"))
+	_, _ = fmt.Fprintf(out, "[docker_entrypoint:%s] [pid %d] DOCKERE: ", severity, os.Getpid())
+	_, _ = fmt.Fprintf(out, format, a...)
+
+	_, _ = fmt.Fprintln(out)
+	_ = out.Flush()
+}