Cannot connect to AWS Mqtt endpoint inside docker container - docker

I am using the AWS IOT SDK java client to connect to an AWS Mqtt endpoint. If run it locally, it works fine.
Then I wrap up my application inside a docker container and use docker-compose to run it, the application just stuck at where it try to make the connection to the endpoing.
However, if I change the docker container's network mode to host:
network_mode: "host"
It works again.
So I guess there is something wrong with the container network configuration. Do I need to expose any ports specific to the Mqtt (like port 443?) But that does not work as well.
Updated the network setting below:
[
{
"Name": "2234_emulator",
"Id": "af69dba44fc91922e50c883c80852c0be2d6a87218e5d9821a1331547d39e343",
"Created": "2022-02-12T14:23:19.298315542Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.20.0.0/16"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"0dc64743c4643d972ae5bc9010416880321bb2fde8ad3afd6834fa6d1eaa0cf6": {
"Name": "2234_ScannerService_1",
"EndpointID": "1c362f48ec0f4afcd1fe705103c0867fe54d874ddb42f678580edcaf0a23e892",
"MacAddress": "02:42:ac:14:00:02",
"IPv4Address": "172.20.0.2/16",
"IPv6Address": ""
},
"5d79cb8e56f7a7789f1860bfc0f48077b326736762c2c13238883bac2a5b40d1": {
"Name": "2234_DeviceEmulatorService_1",
"EndpointID": "8f4170c876d527edb22c4ff47ff167d28b86eeb10c78943fdfedd086237c8c26",
"MacAddress": "02:42:ac:14:00:0f",
"IPv4Address": "172.20.0.15/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.network": "emulator",
"com.docker.compose.project": "2234",
"com.docker.compose.version": "1.27.0"
}
},
{
"Name": "2234_main",
"Id": "b588bb5a545ae0e82f8d13f693d6447024ccf475428e18f31caa7bb4eb9c6102",
"Created": "2022-02-12T14:23:19.205307729Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.128.0/20",
"Gateway": "192.168.128.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"0cca77c4db7b0a12d2d61e7cfc2d2357a8dc4214997ec212340331def380c235": {
"Name": "2234_ServiceA_1",
"EndpointID": "15d775a2692032800d986390ee2a2b672466c00172dd3cd334fa1f16096ca0b4",
"MacAddress": "02:42:c0:a8:80:09",
"IPv4Address": "192.168.128.9/20",
"IPv6Address": ""
},
"0dc64743c4643d972ae5bc9010416880321bb2fde8ad3afd6834fa6d1eaa0cf6": {
"Name": "2234_ServiceA_1",
"EndpointID": "134a2b629c98420a80575e622299acd11a03d9cb150aa68c7d71ef942950fa5a",
"MacAddress": "02:42:c0:a8:80:0e",
"IPv4Address": "192.168.128.14/20",
"IPv6Address": ""
},
"148494a3f1e0b2d182adc735cace01c91e2f3c365009f476b86503c87b8903fb": {
"Name": "2234_ServiceA_1",
"EndpointID": "1ca44d5a3fe1f3d81b9a03eaf89a8cd7fc343e0cdc3bfe27a805de2b6cbfd0bb",
"MacAddress": "02:42:c0:a8:80:07",
"IPv4Address": "192.168.128.7/20",
"IPv6Address": ""
},
"1b180c5f62bcd28eb3a28d0c0d682b50080a846f2ccca24a8cf2540f0c95cd6c": {
"Name": "2234_ServiceA_1",
"EndpointID": "730db6763b208d4a6e32c1b20bdd5fc56a0f00340f675411001e05e389235a8f",
"MacAddress": "02:42:c0:a8:80:0f",
"IPv4Address": "192.168.128.15/20",
"IPv6Address": ""
},
"1c3bf13eee59444abcd225637fb6661fb64bac49d0380063b848f9563bbe08b6": {
"Name": "2234_ServiceA_1",
"EndpointID": "585da3c62513f512c6fe2942a4dd8a23c7ff574cc7f8c75ca59ca3e36c369d9e",
"MacAddress": "02:42:c0:a8:80:0c",
"IPv4Address": "192.168.128.12/20",
"IPv6Address": ""
},
"23fc36057ded2b07b4d7963b91960c51a088c4c67a41b4993c11a57f735c91c3": {
"Name": "2234_ServiceA_1",
"EndpointID": "ff36e613c9a8517caafbc5dc37b1b442fad588f0328d2b5cd1902286fd4ecb84",
"MacAddress": "02:42:c0:a8:80:0a",
"IPv4Address": "192.168.128.10/20",
"IPv6Address": ""
},
"2785da15585da3080e6b98b47556b6da191ab8c25b008516654dab0cc06c19e2": {
"Name": "2234_main_1",
"EndpointID": "297c57e418c2e079e41a4b9d1dcfcea60bcfad888d3287465d44c5d00761643f",
"MacAddress": "02:42:c0:a8:80:02",
"IPv4Address": "192.168.128.2/20",
"IPv6Address": ""
},
"27d50157f4e8664756f36233527892e8c4aa2e0afc723f8ba3e23d4820cbd78d": {
"Name": "2234_ServiceA_1",
"EndpointID": "9ca872fb98dd8b9a229cf86975c3e38789679929d7d3e375c292119fdeb4c963",
"MacAddress": "02:42:c0:a8:80:06",
"IPv4Address": "192.168.128.6/20",
"IPv6Address": ""
},
"3260d6123a96496dc0b59984ca95d72db7ae688ea8daad92b7a0fbb47ec56207": {
"Name": "2234_ServiceA_1",
"EndpointID": "037755d88f02225c41be13206e7c406828ef3dff9767939367af43dd1498dd49",
"MacAddress": "02:42:c0:a8:80:0b",
"IPv4Address": "192.168.128.11/20",
"IPv6Address": ""
},
"4b999440f80b9c9e30ced1aba1264f0bed806b30b1a81bcdf3f03f9f4398794e": {
"Name": "2234_ServiceA_1",
"EndpointID": "337baff5222025b7d7ea0c5f490a80d1c4f15dbd8b2e5052d0625bb213a407b0",
"MacAddress": "02:42:c0:a8:80:0d",
"IPv4Address": "192.168.128.13/20",
"IPv6Address": ""
},
"5d79cb8e56f7a7789f1860bfc0f48077b326736762c2c13238883bac2a5b40d1": {
"Name": "2234_ConnectToIotService_1",
"EndpointID": "087108a5226caf371c02ae188d17cd96d464b882ff918fd56d382275e6bb57ab",
"MacAddress": "02:42:c0:a8:80:08",
"IPv4Address": "192.168.128.8/20",
"IPv6Address": ""
},
"6524df811e919b3a4f908f286125af45dfd82a3f4aaf9caeb073915bd4bff12e": {
"Name": "2234_ServiceA_1",
"EndpointID": "d73cb225903e5817c1cf31dee48d3262719935b1cc514407c833e63595ecf2b8",
"MacAddress": "02:42:c0:a8:80:05",
"IPv4Address": "192.168.128.5/20",
"IPv6Address": ""
},
"71c2129a451b66fb9ed25946838f3ecef510cdebc66419c0b060cf15446e606a": {
"Name": "2234_ServiceA_1",
"EndpointID": "3806269285d4c60e0de7a3f87ca83c1cb3244578c43905db0e785999e37872d7",
"MacAddress": "02:42:c0:a8:80:03",
"IPv4Address": "192.168.128.3/20",
"IPv6Address": ""
},
"df8d304e89af7b8972a62334ca76c5e402f9f530c356b40d8d0d52ca189dee47": {
"Name": "2234_ServiceA_1",
"EndpointID": "39f9b5afa2eb6cd5eeaeaaccd03d7594c2b3b0b501399de0d8ea3f9a9e4b92fb",
"MacAddress": "02:42:c0:a8:80:04",
"IPv4Address": "192.168.128.4/20",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.network": "main",
"com.docker.compose.project": "2234",
"com.docker.compose.version": "1.27.0"
}
},
{
"Name": "2234_nginx",
"Id": "61d88a21886d9377a8c67b184a4d8a99725ef3b67ec8c2d67dc22de9c271fe96",
"Created": "2022-02-12T14:23:19.2532414Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.144.0/20",
"Gateway": "192.168.144.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"5705f37bb200accee2a1a6a23ba818f89172afab4402809f8f1c6de579437983": {
"Name": "2234_ARAMZLWebAppService_1",
"EndpointID": "b0ea1b5f04ef6ea46332914032dceea21f98deeb161b2c04759e7ec587d1f588",
"MacAddress": "02:42:c0:a8:90:03",
"IPv4Address": "192.168.144.3/20",
"IPv6Address": ""
},
"df8d304e89af7b8972a62334ca76c5e402f9f530c356b40d8d0d52ca189dee47": {
"Name": "2234_web_gateway_1",
"EndpointID": "ecfb032cbd8ab650b7e4cd36c6cfc5035b49a8dc934fc49e4e3a0bf49f5437af",
"MacAddress": "02:42:c0:a8:90:02",
"IPv4Address": "192.168.144.2/20",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.network": "nginx",
"com.docker.compose.project": "2234",
"com.docker.compose.version": "1.27.0"
}
},
{
"Name": "2028970_main",
"Id": "a2cf265e7afddb0691bf2a2b06391a8df0358538cbcc3ffd63823207a3a859ff",
"Created": "2022-02-11T21:43:35.086843314Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.96.0/20",
"Gateway": "192.168.96.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {},
"Options": {},
"Labels": {
"com.docker.compose.network": "main",
"com.docker.compose.project": "2028970",
"com.docker.compose.version": "1.27.0"
}
},
{
"Name": "2028970_nginx",
"Id": "3843388542bc33ef8beb7f81cc599d32b534ade592a8945d62a24ea63aac1d69",
"Created": "2022-02-11T21:43:35.135249579Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.112.0/20",
"Gateway": "192.168.112.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {},
"Options": {},
"Labels": {
"com.docker.compose.network": "nginx",
"com.docker.compose.project": "2028970",
"com.docker.compose.version": "1.27.0"
}
},
{
"Name": "bridge",
"Id": "4fb7977a225db6fa2b8dea7005793a72575cb083b2f997627904a62895cd7f8b",
"Created": "2021-07-29T16:09:49.572103372Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.17.0.0/16",
"Gateway": "172.17.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {},
"Options": {
"com.docker.network.bridge.default_bridge": "true",
"com.docker.network.bridge.enable_icc": "true",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
"com.docker.network.bridge.name": "docker0",
"com.docker.network.driver.mtu": "1500"
},
"Labels": {}
},
{
"Name": "host",
"Id": "adc73d076a994102aa472eb367600c8096aa914297158b10d4b25cd8fa50ed0c",
"Created": "2021-05-11T20:36:17.195375337Z",
"Scope": "local",
"Driver": "host",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": []
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"5af2e9b7e09b87ef226e2f79a2d97c9f81148a4265230758949717f2dd525c97": {
"Name": "2234_IdsService_1",
"EndpointID": "6ce2fdcb4315fa8368435abaaee1f1c41c4f3a771061992225bb0e49b348e24f",
"MacAddress": "",
"IPv4Address": "",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
},
{
"Name": "none",
"Id": "ee93bca5bbc6e27bce0cab8380e11a4c3b95a4cc17aaff50a1665b5dcb8a0ecd",
"Created": "2021-05-11T20:36:17.184580174Z",
"Scope": "local",
"Driver": "null",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": []
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {},
"Options": {},
"Labels": {}
}
]

Related

The build in docker dns function is broken suddently

I alway lookup the services each other by docker name in my system, things like : "curl http://contianer_name". Initially, All things is fine and It has worked for several months, But it is broken yesterday, Nginx could not bypass the url like http://contianer_name, And I could not curl successfully for the http://container_name in my host machine. What it is happen? :(,,,
docker network ls:
NETWORK ID NAME DRIVER SCOPE
ecbfafa9fccf bridge bridge local
b1aac67cfbfa myapp-api_default bridge local
5195101110d3 host host local
d90ca5db218d none null local
docker network inspect
[
{
"Name": "myapp-api_default",
"Id": "b1aac67cfbfa2923d5ae88a26e8729159f34e1ae083944e385a23047a7fc7237",
"Created": "2022-09-28T18:21:57.202490009+08:00",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.22.0.0/16",
"Gateway": "172.22.0.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"850c8c091467b7c92aedff5631869ab2f5603ae48ee4a1efb7f18f2f890154ff": {
"Name": "app-boot-system-sample",
"EndpointID": "1497a7ac8726646f24bf82400d69c56bbcacb689d4423ab54db15af586373179",
"MacAddress": "02:42:ac:16:00:05",
"IPv4Address": "172.22.0.5/16",
"IPv6Address": ""
},
"c819074103a5b108d21b836afd1c156036e13f523b44eb5002e13edf48d9f825": {
"Name": "sample-tenant-pc",
"EndpointID": "d4ef531762a117132cbd40dee729cdf2458061e2444d35fc7968411676329e7b",
"MacAddress": "02:42:ac:16:00:04",
"IPv4Address": "172.22.0.4/16",
"IPv6Address": ""
},
"d04e0c550c95da196844c160ca9b9f80f99e3536f92da55d6e9f18533a381802": {
"Name": "sample-event-pc",
"EndpointID": "71bb31e965df8f47cfcc32685594803496bf77ad396854b5dc57851467f99996",
"MacAddress": "02:42:ac:16:00:07",
"IPv4Address": "172.22.0.7/16",
"IPv6Address": ""
},
"ee6589ced2f5080b9f3641104262f430da8f37e1278f094f78a45e2414a607f4": {
"Name": "app-boot-redis-sample",
"EndpointID": "be41952c5709d7a843b9b2ce3276bd7ac8e951ab653ba478d3a8f7cf7fe9599a",
"MacAddress": "02:42:ac:16:00:03",
"IPv4Address": "172.22.0.3/16",
"IPv6Address": ""
},
"fd9196fc0fee67de364d6be37581e4fd9827b2983a332995269af78817828bbd": {
"Name": "sample-org-pc",
"EndpointID": "a0fd805ee5705533f58b7f0e3f1cbdb0a20abc1a01057bd23a2a5161d0c5181c",
"MacAddress": "02:42:ac:16:00:02",
"IPv4Address": "172.22.0.2/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {
"com.docker.compose.network": "myapp-api_default",
"com.docker.compose.project": "myapp-api",
"com.docker.compose.version": "1.26.2"
}
}
]
Docker compose defined as below in the project sample-tenant-pc:
version: '2.4'
services:
sample-tenant-pc:
build:
context: .
restart: always
container_name: sample-tenant-pc
image: sample-tenant-pc
ports:
- 9001:80
networks:
- myapp-api_default
networks:
myapp-api_default:
external: false
name: myapp-api_default

How can I connect one docker container to another via the default bridge network?

I have a python 3.6 app running inside a docker container (linux python3.6 base image), and this app needs to access another container with a redis instance on it. I have both containers running on the default bridge network, and I have configured the first container to point to the second using the second container's IPv4Address:
CELERY_RESULT_BACKEND = redis://172.17.0.3:6379/0
According to the tutorials on docker, this is all you need to connect one container to another when they're running on the same host machine(with no firewalls etc). However, I keep getting a [Errno 111] Connection refused when I try to connect to the redis container. I have checked that the ICC is enabled, and my default bridge network looks like this:
[
{
"Name": "bridge",
"Id": "fda5906e0a6009a5a7dd8839f4d85cdc8de15db34481b7ef15ce66f4343b2f63",
"Created": "2021-03-24T07:54:17.8315909Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.17.0.0/16",
"Gateway": "172.17.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"38beb0863d86dab0f014ef9f1ad85f02efa7fb96520455df6f6ea6b5519f60cc": {
"Name": "local_redis",
"EndpointID": "74f510467dba138f10e1662830060a05ee192c368b32844af73eb4e865fc7182",
"MacAddress": "02:42:ac:11:00:03",
"IPv4Address": "172.17.0.3/16",
"IPv6Address": ""
},
"f314393b25019c8c3084b8cf8465284d5a45c2f48c9aa5c411343e6a5f833c62": {
"Name": "rabbitmq",
"EndpointID": "a4886c398708d5279a8bf0de9dbd8eadd10dd320120243a2ca8c26e0e0c20e16",
"MacAddress": "02:42:ac:11:00:02",
"IPv4Address": "172.17.0.2/16",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.bridge.default_bridge": "true",
"com.docker.network.bridge.enable_icc": "true",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
"com.docker.network.bridge.name": "docker0",
"com.docker.network.driver.mtu": "1500"
},
"Labels": {}
}
]
Any help would be much appreciated.

Docker: Can't remove macvlan configuration network

Using portainer, I created a macvlan configuration network. Now, I want to remove this network. However, for some reason, I can't. I do receive the following error msg: Error response from daemon: error while removing network: configuration network "my_macvlan_config" is in use.
The weird thing is that I don't think that the network is in use. There is no container attached to it. When inspecting the network, I get the following results:
~$ sudo docker network inspect my_macvlan_config
[
{
"Name": "my_macvlan_config",
"Id": "5d95270684516484632c4505e15ba8253bbe8d780b2c41a84a07fbbe09d7a9b6",
"Created": "2020-05-18T20:59:03.472260896+02:00",
"Scope": "local",
"Driver": "null",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.13.0/24",
"IPRange": "192.168.13.200/29",
"Gateway": "192.168.13.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": true,
"Containers": {},
"Options": {
"parent": "eth0"
},
"Labels": {}
}
]
Docker itself is running on my Synology Diskstation, fwiw.
EDIT:
There's another network called macvlan that is connected to my_macvlan_config.
~$ sudo docker network inspect macvlan
[
{
"Name": "macvlan",
"Id": "8a831afa776475b01ca240f4b6b2434c820b8a03910b402760e3cd988e7ddb5c",
"Created": "2020-05-23T23:11:17.738229138+02:00",
"Scope": "local",
"Driver": "macvlan",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.13.0/24",
"IPRange": "192.168.13.210/29",
"Gateway": "192.168.13.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": "macvlan_config"
},
"ConfigOnly": false,
"Containers": {
"6f025749fe99a22fa3729bebfa72d6329b363fe8f6589d9147d0d58a9934dd42": {
"Name": "tvheadend",
"EndpointID": "bc827cb2fddc4374fde7634534efd0c8c110af5a70aa9b16a319b770dfe7a0f2",
"MacAddress": "02:42:c0:a8:0d:d3",
"IPv4Address": "192.168.13.211/24",
"IPv6Address": ""
}
},
"Options": {
"parent": "eth0"
},
"Labels": {}
}
]
And there's one more network, which is apparently unrelated.
~$ sudo docker network inspect macvlan_config
[
{
"Name": "macvlan_config",
"Id": "644a15c6b9e653ec3f48c4a2e290f996b41361170d5ab63053b87a301168345f",
"Created": "2020-05-23T23:10:54.880348491+02:00",
"Scope": "local",
"Driver": "null",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "192.168.13.0/24",
"IPRange": "192.168.13.210/29",
"Gateway": "192.168.13.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": true,
"Containers": {},
"Options": {
"parent": "eth0"
},
"Labels": {}
}
]
I then removed the tvheadend container. I was then able to delete all networks but my_macvlan_config.

How to use docker hostname when running a container

I'm runnig RabbitMQ in docker
>docker run -d --hostname my-rabbit --name some-rabbit --rm --network my-bridge rabbitmq
My container name is some-rabbit and my hostname is my-rabbit
The container is connected to my-bridge network
My app is also connected to my-bridge network
docker network inspect my-bridge produces:
[
{
"Name": "my-bridge",
"Id": "c996f5318b2b3ff907b6680e41c4551f184f2c43b0df43fd6916fa8d1707e427",
"Created": "2018-12-26T19:40:46.6982856Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "172.21.0.0/16",
"Gateway": "172.21.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"98d81ba991febbc9dc0775effc79a2b083f62fe563aad3ce146e56bab5b09f4c": {
"Name": "some-rabbit",
"EndpointID": "acb3da3e91d655a3ed245fa3938edd681318129e514b83db07e1b4efd4f2bfc2",
"MacAddress": "02:42:ac:15:00:02",
"IPv4Address": "172.21.0.2/16",
"IPv6Address": ""
},
"9fdf456e352e932b13530223f736028f357e63ead5ace042a13200f6d5744d62": {
"Name": "dockercompose8897046891659778892_publisher_1",
"EndpointID": "f45ba7f9c7832d3514d22ddf29bc19f1e74529cb371b335542c9eb54469fe7a4",
"MacAddress": "02:42:ac:15:00:04",
"IPv4Address": "172.21.0.4/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
}
]
docker inspect some-rabbit produces:
...
"Config": {
"Hostname": "my-rabbit",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"25672/tcp": {},
"4369/tcp": {},
"5671/tcp": {},
"5672/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/lib/rabbitmq/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"GOSU_VERSION=1.10",
"RABBITMQ_LOGS=-",
"RABBITMQ_SASL_LOGS=-",
"RABBITMQ_GPG_KEY=0A9AF2115F4687BD29803A206B73A36E6026DFCA",
"RABBITMQ_VERSION=3.7.8",
"RABBITMQ_GITHUB_TAG=v3.7.8",
"RABBITMQ_DEBIAN_VERSION=3.7.8-1",
"LANG=C.UTF-8",
"HOME=/var/lib/rabbitmq"
],
"Cmd": [
"rabbitmq-server"
],
"ArgsEscaped": true,
"Image": "rabbitmq",
"Volumes": {
"/var/lib/rabbitmq": {}
},
"WorkingDir": "",
"Entrypoint": [
"docker-entrypoint.sh"
],
"OnBuild": null,
"Labels": {}
},
"NetworkSettings": {
"Bridge": "",
"SandboxID": "bac2e155323c1ec94e145a37f45f8bc0d32e28a2b363cb1c9f3d4ed922a91a56",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {
"25672/tcp": null,
"4369/tcp": null,
"5671/tcp": null,
"5672/tcp": null
},
"SandboxKey": "/var/run/docker/netns/bac2e155323c",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "",
"Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "",
"IPPrefixLen": 0,
"IPv6Gateway": "",
"MacAddress": "",
"Networks": {
"my-bridge": {
"IPAMConfig": null,
"Links": null,
"Aliases": [
"98d81ba991fe"
],
"NetworkID": "c996f5318b2b3ff907b6680e41c4551f184f2c43b0df43fd6916fa8d1707e427",
"EndpointID": "acb3da3e91d655a3ed245fa3938edd681318129e514b83db07e1b4efd4f2bfc2",
"Gateway": "172.21.0.1",
"IPAddress": "172.21.0.2",
"IPPrefixLen": 16,
"IPv6Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"MacAddress": "02:42:ac:15:00:02",
"DriverOpts": null
}
}
}
}
]
Concluding:
Both rabbitmq and my app are running in the same network
RabbitMQ has a custom hostname my-rabbit which can be observed when inspecting the container: "Hostname": "my-rabbit"
However when my app is trying to reach RabbitMQ at address my-rabbit, connection fails. Only if I use the container name as the address (some-rabbit) it works.
Is my understanding of --hostname wrong or am I using it wrong? When is it useful to use custom --hostname?

Hostname is only visible to the application inside that same container. Docker's embedded DNS will not resolve container hostnames. What you can resolve with docker's DNS are:
container name
container id
network alias for a container (including the service name in a compose file)

What IP address to use to connect to container in network?

[
{
"Name": "composer_default",
"Id": "1b06e8bd3c547c739285284f89d416b6bae6cad8d8a5437659cc2877136c5e8f",
"Created": "2018-05-25T06:42:35.269643488Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"1963ad6763c63f3e4dd15b0a4717ddee5c2fe39dad90edbd75c4a0c4f412439b": {
"Name": "orderer.example.com",
"EndpointID": "a34529bb554dd0a7f3ad706cf95536112774b209619364dd98f7edbb5317b150",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
},
"46237b2a21b2a2dbb513ccea7e93793538bcdeaf583e82911c2451f7ee109faf": {
"Name": "couchdb",
"EndpointID": "398a01a0f85cf91ddb23933ded579597263135cbe5b027a73d9bbe374837a06f",
"MacAddress": "02:42:ac:12:00:04",
"IPv4Address": "172.18.0.4/16",
"IPv6Address": ""
},
"5baee4bb30d087b0d622954228be91509124f632a81774fb382fe0e80111d32b": {
"Name": "ca.org1.example.com",
"EndpointID": "a458f59f8d3fa2600f6eb933ee685bffc08ac83cd793ad707f9188b1a07fb6a9",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
},
"651d6d2878104cc496b0bafd6466b70d8a45ef462cc06130e93e0a50214d1f99": {
"Name": "peer0.org1.example.com",
"EndpointID": "9e9a7c2c3164d6258e5bd3231376772703fe2d621978e0760e44569fc3c8c567",
"MacAddress": "02:42:ac:12:00:05",
"IPv4Address": "172.18.0.5/16",
"IPv6Address": ""
},
"da6a8ade513c4fb9b1a351f42e0a06f2e26f0eb471fa08832aa3863285e2f384": {
"Name": "dev-peer0.org1.example.com-usps-imts-network-0.0.2",
"EndpointID": "0f73549d1c16abb13fe1a2d1a1a175e6161ad3d155064033654a436669468b9e",
"MacAddress": "02:42:ac:12:00:06",
"IPv4Address": "172.18.0.6/16",
"IPv6Address": ""
}
},
"Options": {},
"Labels": {}
}
]
I have another Node.js app in a container that I will add to this composer_default network. orderer.example.com is also in this network in its own container. When Node.js app was outside of container, I was previously doing grpc://localhost:7050 to connect.
Now that it is in a container, grpc://<WHAT-IP-SHOULD-I-USE>:7050?
I tried the container name grpc://orderer.example.com:7050, as well the network gateway grpc://172.18.0.1:7050, and am unable to connect.

Container name or IP should work so http:localhost:7050 => http://orderer.example.com:7050 or http://172.18.0.3:7050.
{
"name":"hlfv1",
"x-type":"hlfv1",
"x-commitTimeout":300,
"version":"1.0.0",
"client":{
"organization":"Org1",
"connection":{
"timeout":{
"peer":{
"endorser":"300",
"eventHub":"300",
"eventReg":"300"
},
"orderer":"300"
}
}
},
"channels":{
"composerchannel":{
"orderers":[
"orderer.example.com"
],
"peers":{
"peer0.org1.example.com":{
}
}
}
},
"organizations":{
"Org1":{
"mspid":"Org1MSP",
"peers":[
"peer0.org1.example.com"
],
"certificateAuthorities":[
"ca.org1.example.com"
]
}
},
"orderers":{
"orderer.example.com":{
"url":"grpc://orderer.example.com:7050"
}
},
"peers":{
"peer0.org1.example.com":{
"url":"grpc://peer0.org1.example.com:7051",
"eventUrl":"grpc://peer0.org1.example.com:7053"
}
},
"certificateAuthorities":{
"ca.org1.example.com":{
"url":"http://ca.org1.example.com:7054",
"caName":"ca.org1.example.com"
}
}
}

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