I've defined a bunch of delayed message which must publish exactly at the time and order.

$delayed/143/test => idx = 1
$delayed/168/test => idx = 2
$delayed/193/test => idx = 3
$delayed/218/test => idx = 4
$delayed/243/test => idx = 5
$delayed/268/test => idx = 6
$delayed/293/test => idx = 7
$delayed/318/test => idx = 8
$delayed/343/test => idx = 9
$delayed/368/test => idx = 10

all the messages are qos 1 and have specific index in the payload for debug purpose. The first message must be published at 11:50:00 and after that messages must be published each 25 seconds in order.
I subscribe into test topic with web dashboard and got all messages as I expected but not in time and not in order!

the order that I got messages:

idx: 3 at 11:50:49
idx: 9 at 11:53:19
idx: 1 at 11:53:20
idx: 10 at 11:53:44
idx: 2 at 11:53:44
idx: 6 at 11:53:44
idx: 7 at 11:53:44
idx: 8 at 11:53:44
idx: 4 at 11:53:44
idx: 5 at 11:53:44

1. Support to cancel the delayed messages
2. Query the messages in delayed publish queue

Emqx v3.0.1 Cluster Environment is running under CentOS 7.4.1 with two nodes:
node-1: [email protected]
node-2: [email protected]

[root@uds-gww2 ~]# /opt/emqx/bin/emqx_ctl cluster status
Cluster status: [{running_nodes,[
'[email protected]',
'[email protected]']}]
[root@uds-gww2 ~]#

[root@uds-gww1 ~]# /opt/emqx/bin/emqx_ctl status
Node '[email protected]' is started
emqx v3.0.1 is running
[root@uds-gww1 ~]#

[root@uds-gww2 ~]# /opt/emqx/bin/emqx_ctl status
Node '[email protected]' is started
emqx v3.0.1 is running
[root@uds-gww2 ~]#

[root@uds-gww1 ~]# cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)
[root@uds-gww1 ~]#

[root@uds-gww2 ~]# cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)
[root@uds-gww2 ~]#

Issue: node-1 "uds-gww1" successfully loaded plugin emqx_delayed_publish, but node-2 "uds-gww2" can not load emqx_delayed_publish. you may see the error below, when I called the command "/opt/emqx/bin/emqx_ctl plugins load emqx_delayed_publish" .

[root@uds-gww1 ~]# /opt/emqx/bin/emqx_ctl plugins list | grep emqx_delayed_publish
Plugin(emqx_delayed_publish, version=3.0, description=EMQ X Delayed Publish, active=true)
[root@uds-gww1 ~]#

[root@uds-gww2 ~]# /opt/emqx/bin/emqx_ctl plugins list | grep emqx_delayed_publish
Plugin(emqx_delayed_publish, version=3.0, description=EMQ X Delayed Publish, active=false)
[root@uds-gww2 ~]#

[root@uds-gww2 ~]# /opt/emqx/bin/emqx_ctl plugins load emqx_delayed_publish
=ERROR REPORT==== 11-Mar-2019::14:17:46.667764 ===
Load plugin emqx_delayed_publish error, cannot start app emqx_delayed_publish for {bad_return,
{{emqx_delayed_publish_app,
start,
[normal,
[]]},
{'EXIT',
{{badmatch,
{error,
{shutdown,
{failed_to_start_child,
delayed_publish,
{{badmatch,
{timeout,
[emqx_delayed_publish]}},
[{emqx_delayed_publish,
init,
1,
[{file,
"src/emqx_delayed_publish.erl"},
{line,
96}]},
{gen_server,
init_it,
2,
[{file,
"gen_server.erl"},
{line,
374}]},
{gen_server,
init_it,
6,
[{file,
"gen_server.erl"},
{line,
342}]},
{proc_lib,
init_p_do_apply,
3,
[{file,
"proc_lib.erl"},
{line,
249}]}]}}}}},
[{emqx_delayed_publish_app,
start,
2,
[{file,
"src/emqx_delayed_publish_app.erl"},
{line,
22}]},
{application_master,
start_it_old,
4,
[{file,
"application_master.erl"},
{line,
277}]}]}}}}
load plugin error: {emqx_delayed_publish,
{bad_return,
{{emqx_delayed_publish_app,start,[normal,[]]},
{'EXIT',
{{badmatch,
{error,
{shutdown,
{failed_to_start_child,delayed_publish,
{{badmatch,{timeout,[emqx_delayed_publish]}},
[{emqx_delayed_publish,init,1,
[{file,"src/emqx_delayed_publish.erl"},
{line,96}]},
{gen_server,init_it,2,
[{file,"gen_server.erl"},{line,374}]},
{gen_server,init_it,6,
[{file,"gen_server.erl"},{line,342}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,249}]}]}}}}},
[{emqx_delayed_publish_app,start,2,
[{file,"src/emqx_delayed_publish_app.erl"},
{line,22}]},
{application_master,start_it_old,4,
[{file,"application_master.erl"},{line,277}]}]}}}}}
[root@uds-gww2 ~]#

So, How I could enable emqx_delayed_publish in both two nodes ? Thanks !