Tutorial

You can use nats-top to monitor in realtime NATS server connections and message statistics.

Prerequisites

1. Install nats-top

% go get github.com/nats-io/nats-top

You may need to run the following instead:

% sudo -E go get github.com/nats-io/nats-top

2. Start the NATS server with monitoring enabled

% nats-server -m 8222

3. Start nats-top

% 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