我在现场拥有强大的双核 IoT 网关，带有高速蜂窝调制解调器和良好的互联网连接，但它们无法将 2.5 KB MQTT 消息发送到我的 AWS IoT 消息代理。我的程序发送各种大小的消息，0.1 KB 或 0.2 KB 的消息成功率超过 99%。1.5 KB 的消息大约是 50/50，而 2.5 KB 的消息成功率不到 10%……如果我不看它们（它变得更奇怪）。
我的网关将在几天内无法发送 2.5 KB 消息（一直成功发送较小的 0.1 KB 和 1.5 KB 消息），但是一旦我使用 OpenVPN VPN 进入网关进行调查，它立即发送2.5 KB 的消息。这就像让我的孩子在我不在的时候做点什么；我一回来，马上就完成了……太奇怪了，太令人沮丧了！！
因此，我猜这与我的网关的互联网连接有关。我可以在它们上流式传输 Netflix 电影，但它们无法发送 2.5 KB MQTT 消息……当我在它们上安装软件时，它们可以在几秒钟内下载数兆字节的数据。我还猜测它不是 AWS IoT，因为当我从我的开发计算机重现问题时，2.5 KB 消息总是成功发布到 AWS IoT 消息代理。
580 美元的网关规格：
- Axiomtek ICO120 双核 x86
- Ubuntu Linux 18.04 LTS
- SIMCom SIM7600AH 调制解调器
使用 Paho MQTT 库连接到 AWS IoT 消息代理的 Python 代码：
class PahoContainer:
def __init__(
self,
c,
mqtt_broker,
cert_dir="/home/user/certs",
set_on_message=True,
set_on_publish=True,
aws_thing=None,
set_will=True,
):
"""Connects a client to MQTT broker"""
self.c = c
self.mqtt_broker = mqtt_broker
self.cert_dir = cert_dir
self.set_on_message = set_on_message
self.set_on_publish = set_on_publish
self.aws_thing = aws_thing
self.connect(set_will=set_will)
def on_connect(self, client, userdata, flags, rc):
"""The callback for when the client receives a CONNACK response from the server."""
self.c.logger.info(f"Paho connected with result code: {rc}")
# If the result code == 0 == True, set the connected_flag = True
if rc == 0:
self.c.logger.info(f"Setting Paho client.connected_flag = True")
client.connected_flag = True
def on_disconnect(self, client, userdata, rc):
"""
The callback for a disconnection. You will need to reconnect as soon as possible.
Since we run a network loop using loop_start() or loop_forever(), the re-connections are automatically handled.
A new connection attempt is made automatically in the background every 3 to 6 seconds.
"""
self.c.logger.info(f"on_disconnect callback. Disconnection reason rc: '{rc}'")
client.connected_flag = False
client.disconnect_flag = True
def on_message(self, client, userdata, msg):
"""The callback for when a PUBLISH message is received from the server"""
self.c.logger.info(f"Paho msg.topic: {msg.topic}; str(msg.payload): {str(msg.payload)}")
def on_publish(self, client, userdata, mid):
"""The callback for when a PUBLISH message is sent to the server"""
self.c.logger.info(f"Paho on_publish callback for Message ID (mid): {mid}")
def on_log(self, client, userdata, level, buf):
"""Callback to record log messages"""
self.c.logger.info(f"on_log callback. Level: '{level}'; msg buf: '{buf}'")
def try_connecting(self, broker, port, keepalive, try_x_times=20):
"""Try connecting up to 20 times before raising an error"""
counter = 0
while True:
counter += 1
try:
self.client.connect(broker, port=port, keepalive=keepalive)
except Exception:
x_more_times = try_x_times - counter
if x_more_times == 0:
raise
self.c.logger.exception(f"Problem connecting. Will try again {x_more_times}...")
time.sleep(0.1)
else:
break
def connect(self, set_will=True):
"""Connect to the message broker server"""
client_id = mqtt.base62(uuid.uuid4().int, padding=22)
self.client = mqtt.Client(client_id=client_id, clean_session=True)
# Set a will to be sent by the broker in case the client disconnects unexpectedly.
# This must be called before connect() to have any effect.
# topic: The topic that the will message should be published on.
# payload: The message to send as a will. If not given, or set to None a
# zero length message will be used as the will.
if set_will:
if self.aws_thing is None:
self.c.logger.warning("set_will is True but there is no self.aws_thing, so it can't happen")
else:
topic_lwt = f'last_will/{self.aws_thing.upper()}'
payload_lwt = json.dumps({"connected": 0})
self.client.will_set(topic_lwt, payload=payload_lwt, qos=1, retain=False)
# We MUST use this on_connect callback to set the client.connected_flag = True.
# Otherwise we'll be in an infinite loop
self.client.on_connect = self.on_connect
self.client.on_disconnect = self.on_disconnect
# Enable logging using the standard python logging package.
# This may be used at the same time as the on_log callback method
# If logger is specified (default logger=None), then that logging.Logger object will be used;
# otherwise one will be created automatically
self.client.enable_logger(logger=self.c.logger)
# self.client.enable_logger(logger=None)
# Set the log level, if logger=None in enable_logger()
self.client._logger.setLevel(logging.DEBUG)
self.client.on_log = self.on_log
# The client will automatically retry connection.
# Between each attempt it will wait a number of seconds between min_delay and max_delay
# When the connection is lost, initially the reconnection attempt is delayed of min_delay seconds.
# It's doubled between subsequent attempt up to max_delay.
# The delay is reset to min_delay when the connection complete (e.g. the CONNACK is received,
# not just the TCP connection is established).
self.client.reconnect_delay_set(min_delay=1, max_delay=5)
# Set the maximum number of messages with QoS>0 that can be part way through their network flow at once.
# Defaults to 20. Increasing this value will consume more memory but can increase throughput
self.client.max_inflight_messages_set(10)
# Set the maximum number of outgoing messages with QoS>0 that can be pending in the outgoing message queue.
# Defaults to 0. 0 means unlimited. When the queue is full, any further outgoing messages would be dropped.
self.client.max_queued_messages_set(0)
# Set the time in seconds before a message with QoS>0 is retried, if the broker does not respond.
# This is set to 5 seconds by default and should not normally need changing.
self.client.message_retry_set(2)
if self.set_on_message:
self.client.on_message = self.on_message
if self.set_on_publish:
self.client.on_publish = self.on_publish
# Initialize client.connected_flag = False
self.client.connected_flag = False
self.c.logger.info(f"Connecting to broker: {self.mqtt_broker}")
self.root_ca, self.device_cert, self.private_key = get_certs(self.c, self.cert_dir)
self.client.tls_set(
ca_certs=self.root_ca,
certfile=self.device_cert,
keyfile=self.private_key,
cert_reqs=ssl.CERT_REQUIRED,
tls_version=ssl.PROTOCOL_TLSv1_2,
ciphers=None,
)
self.try_connecting(
self.mqtt_broker,
port=8883,
keepalive=60,
try_x_times=20
)
# We must start the loop before the while not client.connected_flag loop
self.client.loop_start()
# If we are not connected yet, wait a bit, then try again before returning the client
while not self.client.connected_flag:
seconds_to_sleep = 0.05
self.c.logger.info(
f"Waiting {seconds_to_sleep} seconds, then checking client.connected_flag again"
)
time.sleep(seconds_to_sleep)
向 AWS IoT 发送消息的简单代码：
# The metrics_dict is a Python dictionary with 2.5 KB of key/value pairs
payload = json.dumps({"metrics": metrics_dict})
info = paho_container.client.publish(
topic,
payload,
qos=1,
)
用于创建 GSM 蜂窝网络连接的 Linux 网络管理器 (nmcli) 命令：
sudo nmcli radio wwan on
sudo nmcli c add type gsm ifname '*' con-name 'my_conn' apn 'pda.bell.ca' connection.autoconnect yes ipv4.dns '8.8.8.8 8.8.4.4'
sudo nmcli c up
2021 年 1 月 26 日编辑：
ifconfig tun0OpenVPN 连接命令的输出（我已经更改了 IP 地址）：
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500
inet 172.27.abc.def netmask 255.255.248.0 destination 172.27.abc.def
inet6 fe80::4597:4b9f:abcd:efgh prefixlen 64 scopeid 0x20<link>
unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 txqueuelen 100 (UNSPEC)
RX packets 9235 bytes 2655505 (2.6 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 9768 bytes 3329110 (3.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
ifconfig wwp0s21f0u4i5GSM 蜂窝连接命令的输出，显示 MTU 为 1500 字节（我已更改 IP 地址）：
wwp0s21f0u4i5: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500
inet 174.90.ghi.jkl netmask 255.255.255.248 destination 174.90.ghi.jkl
unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 txqueuelen 1000 (UNSPEC)
RX packets 11784052 bytes 2475908779 (2.4 GB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12009517 bytes 2104615202 (2.1 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
输出nmcli c s user_apn（我更改了 IP 地址）：
$ nmcli c s user_apn
connection.id: user_apn
connection.uuid: 05ebc6d3-4fbb-4ddb-93fd-25fb57314ca2
connection.stable-id: --
connection.type: gsm
connection.interface-name: cdc-wdm0
connection.autoconnect: yes
connection.autoconnect-priority: 0
connection.autoconnect-retries: -1 (default)
connection.auth-retries: -1
connection.timestamp: 1611695541
connection.read-only: no
connection.permissions: --
connection.zone: --
connection.master: --
connection.slave-type: --
connection.autoconnect-slaves: -1 (default)
connection.secondaries: --
connection.gateway-ping-timeout: 0
connection.metered: unknown
connection.lldp: default
connection.mdns: -1 (default)
ipv4.method: auto
ipv4.dns: 8.8.8.8,8.8.4.4
ipv4.dns-search: --
ipv4.dns-options: ""
ipv4.dns-priority: 0
ipv4.addresses: --
ipv4.gateway: --
ipv4.routes: --
ipv4.route-metric: -1
ipv4.route-table: 0 (unspec)
ipv4.ignore-auto-routes: no
ipv4.ignore-auto-dns: no
ipv4.dhcp-client-id: --
ipv4.dhcp-timeout: 0 (default)
ipv4.dhcp-send-hostname: yes
ipv4.dhcp-hostname: --
ipv4.dhcp-fqdn: --
ipv4.never-default: no
ipv4.may-fail: yes
ipv4.dad-timeout: -1 (default)
ipv6.method: auto
ipv6.dns: --
ipv6.dns-search: --
ipv6.dns-options: ""
ipv6.dns-priority: 0
ipv6.addresses: --
ipv6.gateway: --
ipv6.routes: --
ipv6.route-metric: -1
ipv6.route-table: 0 (unspec)
ipv6.ignore-auto-routes: no
ipv6.ignore-auto-dns: no
ipv6.never-default: no
ipv6.may-fail: yes
ipv6.ip6-privacy: -1 (unknown)
ipv6.addr-gen-mode: stable-privacy
ipv6.dhcp-send-hostname: yes
ipv6.dhcp-hostname: --
ipv6.token: --
gsm.number: *99#
gsm.username: --
gsm.password: <hidden>
gsm.password-flags: 0 (none)
gsm.apn: wrmstatic.bell.ca.ioe
gsm.network-id: --
gsm.pin: <hidden>
gsm.pin-flags: 0 (none)
gsm.home-only: no
gsm.device-id: --
gsm.sim-id: --
gsm.sim-operator-id: --
gsm.mtu: auto
proxy.method: none
proxy.browser-only: no
proxy.pac-url: --
proxy.pac-script: --
GENERAL.NAME: user_apn
GENERAL.UUID: 05ebc6d3-4fbb-4ddb-93fd-25fb57314ca2
GENERAL.DEVICES: cdc-wdm0
GENERAL.STATE: activated
GENERAL.DEFAULT: yes
GENERAL.DEFAULT6: no
GENERAL.SPEC-OBJECT: --
GENERAL.VPN: no
GENERAL.DBUS-PATH: /org/freedesktop/NetworkManager/ActiveConnection/1
GENERAL.CON-PATH: /org/freedesktop/NetworkManager/Settings/1
GENERAL.ZONE: --
GENERAL.MASTER-PATH: --
IP4.ADDRESS[1]: 174.90.123.456/29
IP4.GATEWAY: 174.90.123.457
IP4.ROUTE[1]: dst = 174.90.123.452/29, nh = 0.0.0.0, mt = 700
IP4.ROUTE[2]: dst = 169.254.0.0/16, nh = 0.0.0.0, mt = 1000
IP4.ROUTE[3]: dst = 54.218.161.180/32, nh = 174.90.186.221, mt = 0
IP4.ROUTE[4]: dst = 0.0.0.0/0, nh = 174.90.186.221, mt = 700
IP4.DNS[1]: 70.28.245.227
IP4.DNS[2]: 184.151.118.254
IP4.DNS[3]: 8.8.8.8
IP4.DNS[4]: 8.8.4.4
IP6.GATEWAY: --
编辑 2021 年 1 月 27 日上午 9:00 MST：输出 traceroute --mtu <broker>
试图弄清楚这是否是与 1500 的 MTU 相关的数据包碎片问题以及 MQTT 消息在 1.5 KB 大小左右开始失败的事实，并且几乎总是在 2.5 KB 大小时失败。
$ traceroute --mtu abcdefg-ats.iot.us-west-2.amazonaws.com
traceroute to abcdefg-ats.iot.us-west-2.amazonaws.com (52.43.abc.def), 30 hops max, 65000 byte packets
1 172.27.abc.def (172.27.abc.def) 78.980 ms F=1500 75.051 ms 77.459 ms
2 ec2-50-112-abc-def.us-west-2.compute.amazonaws.com (50.112.abc.def) 101.733 ms ec2-34-221-abc-def.us-west-2.compute.amazonaws.com (34.221.abc.def) 78.166 ms ec2-50-112-abc-def.us-west-2.compute.amazonaws.com (50.112.abc.def) 93.053 ms
3 * * *
4 * * *
5 * * *
6 * * *
7 * * *
8 * * *
9 * * *
10 * * *
11 * * *
12 * * *
13 * * *
14 * * *
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
21 * * *
22 * * *
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *
编辑 2021 年 1 月 27 日上午 9:50 MST 显示ping命令输出：
当我用 1300 字节 ping AWS IoT 消息代理时，它每次都通过：
$ ping -c 3 -s 1300 52.43.abc.def
PING 52.43.abc.def (52.43.abc.def) 1300(1328) bytes of data.
1308 bytes from 52.43.abc.def: icmp_seq=1 ttl=253 time=87.7 ms
1308 bytes from 52.43.abc.def: icmp_seq=2 ttl=253 time=99.7 ms
1308 bytes from 52.43.abc.def: icmp_seq=3 ttl=253 time=106 ms
但是，当我用 1400 字节 (1.4 KB) ping 代理时，它超时了！为什么？
$ ping -c 3 -s 1400 52.43.abc.def
PING 52.43.abc.def (52.43.abc.def) 1400(1428) bytes of data.
--- 52.43.163.79 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2051ms
编辑 1 月 27 日 13:00 MST 显示ip route show输出：
@hardillb 询问“默认路由”是否因 OpenVPN（tun0接口）启动而改变。起初我不确定这意味着什么，但现在我认为 OpenVPN确实改变了默认路由。请参阅以下ip route show引用tun0（OpenVPN 网络接口）的输出：
$ ip route show
0.0.0.0/1 via 172.27.abc.def dev tun0
default via 10.74.abc.def dev wwp0s21f0u4i5 proto static metric 700
10.74.abc.def/30 dev wwp0s21f0u4i5 proto kernel scope link src 10.74.abc.def metric 700
54.218.abc.def via 10.74.abc.def dev wwp0s21f0u4i5
128.0.0.0/1 via 172.27.abc.def dev tun0
169.254.0.0/16 dev enp2s0 scope link metric 1000 linkdown
172.27.abc.def/21 dev tun0 proto kernel scope link src 172.27.abc.def
192.168.2.0/24 dev enp2s0 proto kernel scope link src 192.168.2.2 metric 100 linkdown