Platform sanity checks (#2271)

* Platform sanity checks

* Don't yell about `root` because Docker

setup/base/base.go

@@ -100,6 +100,7 @@ const (
 // The componentName is used for logging purposes, and should be a friendly name
 // of the compontent running, e.g. "SyncAPI"
 func NewBaseDendrite(cfg *config.Dendrite, componentName string, options ...BaseDendriteOptions) *BaseDendrite {
+	platformSanityChecks()
 	useHTTPAPIs := false
 	cacheMetrics := true
 	for _, opt := range options {

setup/base/sanity_other.go

@@ -0,0 +1,8 @@
+//go:build !linux && !darwin && !netbsd && !freebsd && !openbsd && !solaris && !dragonfly && !aix
+// +build !linux,!darwin,!netbsd,!freebsd,!openbsd,!solaris,!dragonfly,!aix
+
+package base
+
+func platformSanityChecks() {
+	// Nothing to do yet.
+}

setup/base/sanity_unix.go

@@ -0,0 +1,22 @@
+//go:build linux || darwin || netbsd || freebsd || openbsd || solaris || dragonfly || aix
+// +build linux darwin netbsd freebsd openbsd solaris dragonfly aix
+
+package base
+
+import (
+	"syscall"
+
+	"github.com/sirupsen/logrus"
+)
+
+func platformSanityChecks() {
+	// Dendrite needs a relatively high number of file descriptors in order
+	// to function properly, particularly when federating with lots of servers.
+	// If we run out of file descriptors, we might run into problems accessing
+	// PostgreSQL amongst other things. Complain at startup if we think the
+	// number of file descriptors is too low.
+	var rLimit syscall.Rlimit
+	if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rLimit); err == nil && rLimit.Cur < 65535 {
+		logrus.Warnf("IMPORTANT: Process file descriptor limit is currently %d, it is recommended to raise the limit for Dendrite to at least 65535 to avoid issues", rLimit.Cur)
+	}
+}