Report how a config reload went: failures, restarts required, and the keys that need one (#1935)

examples/config.yml

@@ -43,7 +43,7 @@ static_host_map:
 
 lighthouse:
   # am_lighthouse is used to enable lighthouse functionality for a node. This should ONLY be true on nodes
-  # you have configured to be lighthouses in your network
+  # you have configured to be lighthouses in your network. Not reloadable.
   am_lighthouse: false
   # serve_dns optionally starts a dns listener that responds to various queries and can even be
   # delegated to for resolution
@@ -126,8 +126,9 @@ lighthouse:
 # Port Nebula will be listening on. The default here is 4242. For a lighthouse node, the port should be defined,
 # however using port 0 will dynamically assign a port and is recommended for roaming nodes.
 listen:
-  # To listen on only ipv4, use "0.0.0.0"
+  # To listen on only ipv4, use "0.0.0.0". Not reloadable.
   host: "::"
+  # Not reloadable.
   port: 4242
   # Sets the max number of packets to pull from the kernel for each syscall (under systems that support recvmmsg)
   # default is 64, does not support reload
@@ -135,7 +136,8 @@ listen:
   # superpacket, so the receive scratch is batch * 64KiB per listening socket (~4MiB per routine at the
   # default of 64). Lower this to trade peak per-syscall throughput for memory on constrained hosts.
   #batch: 64
-  # Linux only. Configure socket buffers for the udp side (outside), leave unset to use the system defaults. Values will be doubled by the kernel
+  # Linux only. Reloadable, but removing a value leaves the socket at the old size until Nebula restarts.
+  # Configure socket buffers for the udp side (outside), leave unset to use the system defaults. Values will be doubled by the kernel
   # Default is net.core.rmem_default and net.core.wmem_default (/proc/sys/net/core/rmem_default and /proc/sys/net/core/rmem_default)
   # Maximum is limited by memory in the system, SO_RCVBUFFORCE and SO_SNDBUFFORCE is used to avoid having to raise the system wide
   # max, net.core.rmem_max and net.core.wmem_max
@@ -179,7 +181,7 @@ listen:
 # Currently, this defaults to 1 which means we have 1 tun queue reader and 1
 # UDP queue reader. Setting this above one will set IFF_MULTI_QUEUE on the tun
 # device and SO_REUSEPORT on the UDP socket to allow multiple queues.
-# This option is only supported on Linux.
+# This option is only supported on Linux. Not reloadable.
 #routines: 1
 
 punchy:
@@ -203,6 +205,7 @@ punchy:
 
 # Cipher allows you to choose between the available ciphers for your network. Options are chachapoly or aes
 # IMPORTANT: this value must be identical on ALL NODES/LIGHTHOUSES. We do not/will not support use of different ciphers simultaneously!
+# Not reloadable.
 #cipher: aes
 
 # Preferred ranges is used to define a hint about the local network ranges, which speeds up discovering the fastest
@@ -234,6 +237,7 @@ punchy:
   # and absolute paths outside of it will be rejected. Default is $TMP/nebula-debug.
   # The directory is NOT automatically created.
   # Overriding this to "" is the same as "/" and will allow overwriting any path on the host.
+  # Not reloadable.
   #sandbox_dir: /var/tmp/nebula-debug
 
 # EXPERIMENTAL: relay support for networks that can't establish direct connections.
@@ -253,19 +257,25 @@ relay:
 # Configure the private interface. Note: addr is baked into the nebula certificate
 tun:
   # When tun is disabled, a lighthouse can be started without a local tun interface (and therefore without root)
+  # Not reloadable.
   disabled: false
   # Name of the device. If not set, a default will be chosen by the OS.
   # For macOS: if set, must be in the form `utun[0-9]+`.
   # For NetBSD: Required to be set, must be in the form `tun[0-9]+`
+  # Not reloadable.
   dev: nebula1
   # Toggles forwarding of local broadcast packets, the address of which depends on the ip/mask encoded in pki.cert
+  # Not reloadable.
   drop_local_broadcast: false
-  # Toggles forwarding of multicast packets
+  # Toggles forwarding of multicast packets. Not reloadable.
   drop_multicast: false
   # Sets the transmit queue length, if you notice lots of transmit drops on the tun it may help to raise this number. Default is 5000
+  # Not reloadable.
   tx_queue: 5000
   # Default MTU for every packet, safe setting is (and the default) 1300 for internet based traffic
   # Anything above 8937, here or on a route below, is capped to 8937 with a warning
+  # Reloadable on Linux only. Where the tun is handed to nebula by a host app (iOS, Android, macOS network extensions)
+  # the host app owns the MTU.
   mtu: 1300
 
   # the use_offloads setting controls if Nebula will attempt to enable GSO and GRO for the tun device. Linux only, not reloadable.
@@ -358,7 +368,7 @@ tun:
   #use_system_route_table: false
   # Buffer size for reading routes updates. 0 means default system buffer size. (/proc/sys/net/core/rmem_default).
   # If using massive routes updates, for example BGP, you may need to increase this value to avoid packet loss.
-  # SO_RCVBUFFORCE is used to avoid having to raise the system wide max
+  # SO_RCVBUFFORCE is used to avoid having to raise the system wide max. Not reloadable.
   #use_system_route_table_buffer_size: 0
 
 # Configure logging level
@@ -408,14 +418,16 @@ logging:
   # Handshakes are sent to all known addresses at each interval with a linear backoff,
   # Wait try_interval after the 1st attempt, 2 * try_interval after the 2nd, etc, until the handshake is older than timeout
   # A 100ms interval with the default 10 retries will give a handshake 5.5 seconds to resolve before timing out
+  # Not reloadable.
   #try_interval: 100ms
   #retries: 20
 
   # query_buffer is the size of the buffer channel for querying lighthouses, drops are recorded in the lighthouse.query.dropped metric.
+  # Not reloadable.
   #query_buffer: 1024
 
   # trigger_buffer is the size of the buffer channel for quickly sending handshakes
-  # after receiving the response for lighthouse queries
+  # after receiving the response for lighthouse queries. Not reloadable.
   #trigger_buffer: 64
 
 # Tunnel manager settings