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Re: [mosquitto-dev] mosquitto sometimes disconnects client after publish
I did not get a packet capture as I don't currently have ssh access to that instance, but am pretty certain it came from the broker. First, I connected directly to the instance, rather than through the load balancer, and the problem persisted. Second, my other client application also saw the issue. Here is a breakdown of what happened:

  • mosquitto and my client started up normally

  • client successfully connects, subscribes to a few topics, and then sends a batch of publishes to various topics (a batch of publishes is about 20 different publishes, each to a different topic, with each message being only 11 bytes)

  • mosquitto sees first batch of publishes from my client

  • mosquitto sees the second batch of publishes from the client 5 minutes later (the interval between batches is 5 minutes)

  • mosquitto does NOT see MOST of third batch of publishes from mqttd at the 10 minute mark. Below are example logs from mosquitto that show only 2 messages get published (out of about 20):

05:38:51
1491370731: Received PUBLISH from zenreach (d0, q0, r0, m0, '2.1/LOC/SMMug3jKfsoLKlXy/LS/PAQ', ... (11 bytes))
05:38:51
1491370731: Received PUBLISH from zenreach (d0, q0, r0, m0, '2.1/LOC/SMMug3jKfsoLKlXy/LS/PAQ', ... (11 bytes))

  • during third batch of publishes, my client starts printing timeout errors on each publish (I'm using WaitTimeout() with a timeout of 5 seconds as shown in my original post)

  • about 15 minutes after the errors started occurring, mosquitto disconnects the client user because of timeout. This makes sense since the keepalive is set to 10 minutes and since mosquitto isn't receiving any publishes (or pings even), it should disconnect the client. Below is the log from mosquitto:

05:53:51
1491371631: Client zenreach has exceeded timeout, disconnecting.
05:53:51
1491371631: Socket error on client zenreach, disconnecting.

The question here is, why do all publishes just suddenly stop working on the 3rd batch (including pings)?


On Tue, Apr 4, 2017 at 9:35 PM cheng <tangch318@xxxxxxxxx> wrote:
Did you capture packet on mosquitto broker side and verify if RESET packet from mosquiito broker?

2017-04-05 1:19 GMT+08:00 Jeff Armstrong <jeff@xxxxxxxxxxxxxxxxx>:
I'm running a mosquitto broker (1.4.10) on AWS behind a ELB. I wrote a client that publishes batches of messages to a single topic. For example, it may send 20 messages of about 5k each, and repeat that every minute.

The first batch of messages always goes through, but subsequent batches are either completely missing or partially missing. I noticed that after a failed batch of messages is published, the client gets disconnected. I can see the TCP reset in the packet capture from the client side. Even though there are no publishing errors, and the disconnect seems to occur AFTER publishing the 2nd batch, the 2nd batch of messages doesn't show up on the broker.

I'm unable to reproduce this running mosquitto locally, which makes it seem like it's a problem with mosquitto specific to AWS or the load balancer. My first thought was that the load balancer was timing out the connections, but the timeout on ELB is 60s, and I set the client keepalive to 5s and the problem persists.

Any ideas?

Thanks,
Jeff
--
Jeff Armstrong
Software Engineer
Greenfield Labs

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--
Jeff Armstrong
Software Engineer
Greenfield Labs

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