You can use nats-top to monitor in realtime NATS server connections and message statistics.
Prerequisites
1. Install nats-top
go install github.com/nats-io/nats-top@latest
You may need to run the following instead:
sudo -E go install github.com/nats-io/nats-top
2. Start the NATS server with monitoring enabled
3. Start nats-top
Result:
nats-server version 0.6.6 (uptime: 2m2s)
Server:
Load: CPU: 0.0% Memory: 6.3M Slow Consumers: 0
In: Msgs: 0 Bytes: 0 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 0 Bytes: 0 Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 0
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
4. Run NATS client programs
Run some NATS client programs and exchange messages.
For the best experience, you will want to run multiple subscribers, at least 2 or 3. Refer to the example pub-sub clients.
5. Check nats-top for statistics
nats-server version 0.6.6 (uptime: 30m51s)
Server:
Load: CPU: 0.0% Memory: 10.3M Slow Consumers: 0
In: Msgs: 56 Bytes: 302 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 98 Bytes: 512 Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:58651 6 1 0 52 0 260 0 go 1.1.0
::1:58922 38 1 0 21 0 105 0 go 1.1.0
::1:58953 39 1 0 21 0 105 0 go 1.1.0
6. Sort nats-top statistics
In nats-top, enter the command o followed by the option, such as bytes_to. You see that nats-top sorts the BYTES_TO column in ascending order.
nats-server version 0.6.6 (uptime: 45m40s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 81 Bytes: 427 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 154 Bytes: 792 Msgs/Sec: 0.0 Bytes/Sec: 0
sort by [bytes_to]:
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:59259 83 1 0 4 0 20 0 go 1.1.0
::1:59349 91 1 0 2 0 10 0 go 1.1.0
::1:59342 90 1 0 0 0 0 0 go 1.1.0
7. Use different sort options
Use some different sort options to explore nats-top, such as:
cid, subs, pending, msgs_to, msgs_from, bytes_to, bytes_from, lang, version
You can also set the sort option on the command line using the -sort flag. For example: nats-top -sort bytes_to.
8. Display the registered subscriptions.
In nats-top, enter the command s to toggle displaying connection subscriptions. When enabled, you see the subscription subject in nats-top table:
nats-server version 0.6.6 (uptime: 1h2m23s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 108 Bytes: 643 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 185 Bytes: 1.0K Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION SUBSCRIPTIONS
::1:59708 115 1 0 6 0 48 0 go 1.1.0 foo.bar
::1:59758 122 1 0 1 0 8 0 go 1.1.0 foo
::1:59817 124 1 0 0 0 0 0 go 1.1.0 foo
9. Quit nats-top
Use the q command to quit nats-top.
10. Restart nats-top with a specified query
For example, to query for the connection with largest number of subscriptions:
nats-top -n 1 -sort subs
Result: nats-top displays only the client connection with the largest number of subscriptions:
nats-server version 0.6.6 (uptime: 1h7m0s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 109 Bytes: 651 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 187 Bytes: 1.0K Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:59708 115 1 0 6 0 48 0 go 1.1.0
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