Function getProxyDERPStartingRegionID

enterprise/coderd/coderd.go:1130–1167

getProxyDERPStartingRegionID returns the starting region ID that should be used for workspace proxies. A proxy's actual region ID is the return value from this function + it's RegionID field. Two ints are returned, the first is the starting region ID for proxies, and the second is the maximum regio

(derpMap *tailcfg.DERPMap)

// Two ints are returned, the first is the starting region ID for proxies, and
// the second is the maximum region ID that already exists in the DERP map.
func getProxyDERPStartingRegionID(derpMap *tailcfg.DERPMap) (sID int64, mID int64) {
	var maxRegionID int64
	for _, region := range derpMap.Regions {
		rid := int64(region.RegionID)
		if rid > maxRegionID {
			maxRegionID = rid
		}
	}
	if maxRegionID < 0 {
		maxRegionID = 0
	}

	// Round to the nearest 10,000 with a sufficient buffer of at least 2,000.
	// The buffer allows for future "fixed" regions to be added to the base DERP
	// map without conflicting with proxy region IDs (standard DERP maps usually
	// use incrementing IDs for new regions).
	//
	// Example:
	//  maxRegionID = -2_000 -> startingRegionID = 10_000
	//  maxRegionID = 8_000 -> startingRegionID = 10_000
	//  maxRegionID = 8_500 -> startingRegionID = 20_000
	//  maxRegionID = 12_000 -> startingRegionID = 20_000
	//  maxRegionID = 20_000 -> startingRegionID = 30_000
	const roundStartingRegionID = 10_000
	const startingRegionIDBuffer = 2_000
	// Add the buffer first.
	startingRegionID := maxRegionID + startingRegionIDBuffer
	// Round UP to the nearest 10,000. Go's math.Ceil rounds up to the nearest
	// integer, so we need to divide by 10,000 first and then multiply by
	// 10,000.
	startingRegionID = int64(math.Ceil(float64(startingRegionID)/roundStartingRegionID) * roundStartingRegionID)
	// This should never be hit but it's here just in case.
	if startingRegionID < roundStartingRegionID {
		startingRegionID = roundStartingRegionID
	}

	return startingRegionID, maxRegionID
}

var (
	lastDerpConflictMutex sync.Mutex