{"action":"created","issue":{"url":"https://api.github.com/repos/moby/moby/issues/30134","repository_url":"https://api.github.com/repos/moby/moby","labels_url":"https://api.github.com/repos/moby/moby/issues/30134/labels{/name}","comments_url":"https://api.github.com/repos/moby/moby/issues/30134/comments","events_url":"https://api.github.com/repos/moby/moby/issues/30134/events","html_url":"https://github.com/moby/moby/issues/30134","id":200653699,"node_id":"MDU6SXNzdWUyMDA2NTM2OTk=","number":30134,"title":"Wrong behaviour of the DNS resolver within Swarm Mode overlay network","user":{"login":"YouriT","id":1449797,"node_id":"MDQ6VXNlcjE0NDk3OTc=","avatar_url":"https://avatars0.githubusercontent.com/u/1449797?v=4","gravatar_id":"","url":"https://api.github.com/users/YouriT","html_url":"https://github.com/YouriT","followers_url":"https://api.github.com/users/YouriT/followers","following_url":"https://api.github.com/users/YouriT/following{/other_user}","gists_url":"https://api.github.com/users/YouriT/gists{/gist_id}","starred_url":"https://api.github.com/users/YouriT/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/YouriT/subscriptions","organizations_url":"https://api.github.com/users/YouriT/orgs","repos_url":"https://api.github.com/users/YouriT/repos","events_url":"https://api.github.com/users/YouriT/events{/privacy}","received_events_url":"https://api.github.com/users/YouriT/received_events","type":"User","site_admin":false},"labels":[{"id":237472034,"node_id":"MDU6TGFiZWwyMzc0NzIwMzQ=","url":"https://api.github.com/repos/moby/moby/labels/area/networking","name":"area/networking","color":"fbca04","default":false},{"id":392678049,"node_id":"MDU6TGFiZWwzOTI2NzgwNDk=","url":"https://api.github.com/repos/moby/moby/labels/area/swarm","name":"area/swarm","color":"fbca04","default":false},{"id":190258329,"node_id":"MDU6TGFiZWwxOTAyNTgzMjk=","url":"https://api.github.com/repos/moby/moby/labels/kind/bug","name":"kind/bug","color":"FF8C94","default":false},{"id":182417459,"node_id":"MDU6TGFiZWwxODI0MTc0NTk=","url":"https://api.github.com/repos/moby/moby/labels/status/more-info-needed","name":"status/more-info-needed","color":"C6A49A","default":false},{"id":375714123,"node_id":"MDU6TGFiZWwzNzU3MTQxMjM=","url":"https://api.github.com/repos/moby/moby/labels/version/1.12","name":"version/1.12","color":"ededed","default":false}],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":64,"created_at":"2017-01-13T15:14:25Z","updated_at":"2018-12-18T03:38:31Z","closed_at":"2018-03-08T11:01:02Z","author_association":"NONE","body":"<!--\r\nIf you are reporting a new issue, make sure that we do not have any duplicates\r\nalready open. You can ensure this by searching the issue list for this\r\nrepository. If there is a duplicate, please close your issue and add a comment\r\nto the existing issue instead.\r\n\r\nIf you suspect your issue is a bug, please edit your issue description to\r\ninclude the BUG REPORT INFORMATION shown below. If you fail to provide this\r\ninformation within 7 days, we cannot debug your issue and will close it. We\r\nwill, however, reopen it if you later provide the information.\r\n\r\nFor more information about reporting issues, see\r\nhttps://github.com/docker/docker/blob/master/CONTRIBUTING.md#reporting-other-issues\r\n\r\n---------------------------------------------------\r\nGENERAL SUPPORT INFORMATION\r\n---------------------------------------------------\r\n\r\nThe GitHub issue tracker is for bug reports and feature requests.\r\nGeneral support can be found at the following locations:\r\n\r\n- Docker Support Forums - https://forums.docker.com\r\n- IRC - irc.freenode.net #docker channel\r\n- Post a question on StackOverflow, using the Docker tag\r\n\r\n---------------------------------------------------\r\nBUG REPORT INFORMATION\r\n---------------------------------------------------\r\nUse the commands below to provide key information from your environment:\r\nYou do NOT have to include this information if this is a FEATURE REQUEST\r\n-->\r\n\r\nI'm trying to setup a mongodb shard with 2 shards and each shards being a replicaset (size=2). I have one mongos router and one replicaset (size=2) of config dbs.\r\n\r\nI was getting plenty of errors about chunks migration and after digging I figured out that the target host was sometimes alive and sometimes not. But the containers where not crashed which was strange.\r\n\r\nAfter digging deeper I figured out that the IP addresses got through the resolution were not right.\r\n\r\nPlease note that each service is running in `dnsrr` mode.\r\n\r\n<!--\r\nBriefly describe the problem you are having in a few paragraphs.\r\n-->\r\n\r\n**Steps to reproduce the issue:**\r\nhard to get exactly the behaviour\r\n1. `docker network create -d overlay public`\r\n2. Create a service within the network on different machines\r\n3. Make the containers crash and let them restart, repeat multiple items\r\n4. Scale the service to 0\r\n5. Place a container within the same network and `nslookup` the service your created earlier\r\n\r\n**Describe the results you received:**\r\n```\r\nnslookup mongo-shard-rs0-2\r\nServer:\t\t127.0.0.11\r\nAddress:\t127.0.0.11#53\r\n\r\nNon-authoritative answer:\r\nName:\tmongo-shard-rs0-2\r\nAddress: 10.0.0.2\r\nName:\tmongo-shard-rs0-2\r\nAddress: 10.0.0.5\r\nName:\tmongo-shard-rs0-2\r\nAddress: 10.0.0.4\r\n```\r\n\r\n**Describe the results you expected:**\r\n```\r\n** server can't find mongo-shard-rs0-2: NXDOMAIN\r\n```\r\n\r\n**Additional information you deem important (e.g. issue happens only occasionally):**\r\nRandom issue. If I restart the machine then it works again. Seems the cache is poisoned or something.\r\n\r\n**Output of `docker version`:**\r\n\r\n```\r\nClient:\r\n Version:      1.12.6\r\n API version:  1.24\r\n Go version:   go1.6.4\r\n Git commit:   78d1802\r\n Built:        Tue Jan 10 20:38:45 2017\r\n OS/Arch:      linux/amd64\r\n\r\nServer:\r\n Version:      1.12.6\r\n API version:  1.24\r\n Go version:   go1.6.4\r\n Git commit:   78d1802\r\n Built:        Tue Jan 10 20:38:45 2017\r\n OS/Arch:      linux/amd64\r\n```\r\n\r\n**Output of `docker info`:**\r\n\r\n```\r\nContainers: 2\r\n Running: 1\r\n Paused: 0\r\n Stopped: 1\r\nImages: 6\r\nServer Version: 1.12.6\r\nStorage Driver: overlay\r\n Backing Filesystem: extfs\r\nLogging Driver: json-file\r\nCgroup Driver: cgroupfs\r\nPlugins:\r\n Volume: local\r\n Network: overlay null bridge host\r\nSwarm: active\r\n NodeID: 0466d9iww2nsv3crnj2yd6vk4\r\n Is Manager: false\r\n Node Address: 172.16.1.13\r\nRuntimes: runc\r\nDefault Runtime: runc\r\nSecurity Options: apparmor seccomp\r\nKernel Version: 4.4.0-59-generic\r\nOperating System: Ubuntu 16.04.1 LTS\r\nOSType: linux\r\nArchitecture: x86_64\r\nCPUs: 2\r\nTotal Memory: 6.65 GiB\r\nName: worker2\r\nID: ZCIH:LHBN:PVQN:O75R:CVMI:R2PK:35O6:ENF6:UTBN:AY2K:IJZQ:DEQK\r\nDocker Root Dir: /var/lib/docker\r\nDebug Mode (client): false\r\nDebug Mode (server): false\r\nRegistry: https://index.docker.io/v1/\r\nWARNING: No swap limit support\r\nLabels:\r\n provider=generic\r\nInsecure Registries:\r\n 127.0.0.0/8\r\n```\r\n\r\n**Additional environment details (AWS, VirtualBox, physical, etc.):**\r\n4 machines running on Ubuntu within OpenStack.\r\n1 manager DRAIN LEADER\r\n2 for `mongod` shards and replicas\r\n1 worker which has `mongos`"},"comment":{"url":"https://api.github.com/repos/moby/moby/issues/comments/448085430","html_url":"https://github.com/moby/moby/issues/30134#issuecomment-448085430","issue_url":"https://api.github.com/repos/moby/moby/issues/30134","id":448085430,"node_id":"MDEyOklzc3VlQ29tbWVudDQ0ODA4NTQzMA==","user":{"login":"leshik","id":443678,"node_id":"MDQ6VXNlcjQ0MzY3OA==","avatar_url":"https://avatars1.githubusercontent.com/u/443678?v=4","gravatar_id":"","url":"https://api.github.com/users/leshik","html_url":"https://github.com/leshik","followers_url":"https://api.github.com/users/leshik/followers","following_url":"https://api.github.com/users/leshik/following{/other_user}","gists_url":"https://api.github.com/users/leshik/gists{/gist_id}","starred_url":"https://api.github.com/users/leshik/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/leshik/subscriptions","organizations_url":"https://api.github.com/users/leshik/orgs","repos_url":"https://api.github.com/users/leshik/repos","events_url":"https://api.github.com/users/leshik/events{/privacy}","received_events_url":"https://api.github.com/users/leshik/received_events","type":"User","site_admin":false},"created_at":"2018-12-18T03:38:31Z","updated_at":"2018-12-18T03:38:31Z","author_association":"NONE","body":"@olljanat sure, here it is:\r\n\r\nFirst, `docker info`:\r\n\r\n```\r\nContainers: 17\r\n Running: 14\r\n Paused: 0\r\n Stopped: 3\r\nImages: 25\r\nServer Version: 18.09.0\r\nStorage Driver: overlay2\r\n Backing Filesystem: extfs\r\n Supports d_type: true\r\n Native Overlay Diff: true\r\nLogging Driver: json-file\r\nCgroup Driver: cgroupfs\r\nPlugins:\r\n Volume: local\r\n Network: bridge host macvlan null overlay\r\n Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog\r\nSwarm: active\r\n NodeID: xbwvu8xd4eovyoaxjwnd1suv6\r\n Is Manager: true\r\n ClusterID: lobvck68wwkolom5c4xfa4vgi\r\n Managers: 1\r\n Nodes: 1\r\n Default Address Pool: 10.0.0.0/8\r\n SubnetSize: 24\r\n Orchestration:\r\n  Task History Retention Limit: 5\r\n Raft:\r\n  Snapshot Interval: 10000\r\n  Number of Old Snapshots to Retain: 0\r\n  Heartbeat Tick: 1\r\n  Election Tick: 10\r\n Dispatcher:\r\n  Heartbeat Period: 5 seconds\r\n CA Configuration:\r\n  Expiry Duration: 3 months\r\n  Force Rotate: 0\r\n Autolock Managers: false\r\n Root Rotation In Progress: false\r\n Node Address: 192.168.1.23\r\n Manager Addresses:\r\n  192.168.1.23:2377\r\nRuntimes: runc\r\nDefault Runtime: runc\r\nInit Binary: docker-init\r\ncontainerd version: c4446665cb9c30056f4998ed953e6d4ff22c7c39\r\nrunc version: 4fc53a81fb7c994640722ac585fa9ca548971871\r\ninit version: fec3683\r\nSecurity Options:\r\n apparmor\r\n seccomp\r\n  Profile: default\r\nKernel Version: 4.15.0-39-generic\r\nOperating System: Ubuntu 18.04.1 LTS\r\nOSType: linux\r\nArchitecture: x86_64\r\nCPUs: 4\r\nTotal Memory: 7.683GiB\r\nName: demo\r\nID: UKKF:U6NR:LIWI:ASCX:LL5L:2KBX:2ARZ:5MMX:M4RI:WQMO:R2UA:F67D\r\nDocker Root Dir: /var/lib/docker\r\nDebug Mode (client): false\r\nDebug Mode (server): false\r\nRegistry: https://index.docker.io/v1/\r\nLabels:\r\nExperimental: false\r\nInsecure Registries:\r\n 127.0.0.0/8\r\nLive Restore Enabled: false\r\nProduct License: Community Engine\r\n\r\nWARNING: No swap limit support\r\n```\r\n\r\nStack compose file `test.yml` for tests:\r\n\r\n```yaml\r\nversion: '3.7'\r\n\r\nservices:\r\n  first:\r\n    image: alpine\r\n    command: sleep 3600\r\n    init: true\r\n\r\n  second:\r\n    image: alpine\r\n    command: sleep 3600\r\n    init: true\r\n```\r\n\r\nThen, `docker stack deploy -c test.yml test`, followed by `docker network inspect test_default`:\r\n\r\n```json\r\n[\r\n    {\r\n        \"Name\": \"test_default\",\r\n        \"Id\": \"quisbu0cbrgz9acy9j808hrxu\",\r\n        \"Created\": \"2018-12-18T10:00:10.846072788+07:00\",\r\n        \"Scope\": \"swarm\",\r\n        \"Driver\": \"overlay\",\r\n        \"EnableIPv6\": false,\r\n        \"IPAM\": {\r\n            \"Driver\": \"default\",\r\n            \"Options\": null,\r\n            \"Config\": [\r\n                {\r\n                    \"Subnet\": \"10.0.5.0/24\",\r\n                    \"Gateway\": \"10.0.5.1\"\r\n                }\r\n            ]\r\n        },\r\n        \"Internal\": false,\r\n        \"Attachable\": false,\r\n        \"Ingress\": false,\r\n        \"ConfigFrom\": {\r\n            \"Network\": \"\"\r\n        },\r\n        \"ConfigOnly\": false,\r\n        \"Containers\": {\r\n            \"39c200af9048f20e2ca50a5e59e2534329134bfd4b270c7b6dcd95119116e86b\": {\r\n                \"Name\": \"test_first.1.qbwe3xsyuiaas50reme2ubtbr\",\r\n                \"EndpointID\": \"3968618c4ac249f82fab75d1c6e68aa8893f3d9cf8279c95f18df924d0271b69\",\r\n                \"MacAddress\": \"02:42:0a:00:05:03\",\r\n                \"IPv4Address\": \"10.0.5.3/24\",\r\n                \"IPv6Address\": \"\"\r\n            },\r\n            \"ccb93d48e2a7e8a6d4c0d0c60872b30f5c4cff43ef97aba4a5aec7118779e612\": {\r\n                \"Name\": \"test_second.1.rermha7mo5sipex53qm6o0s9o\",\r\n                \"EndpointID\": \"d37de1616bc297f9c9b047eeed66f75048f5d9ea2347bcf738fb92eb3623080e\",\r\n                \"MacAddress\": \"02:42:0a:00:05:06\",\r\n                \"IPv4Address\": \"10.0.5.6/24\",\r\n                \"IPv6Address\": \"\"\r\n            },\r\n            \"lb-test_default\": {\r\n                \"Name\": \"test_default-endpoint\",\r\n                \"EndpointID\": \"90df88a051eaf6557bf22883a6659044826d288f41559728ba5b13d6b5efed36\",\r\n                \"MacAddress\": \"02:42:0a:00:05:04\",\r\n                \"IPv4Address\": \"10.0.5.4/24\",\r\n                \"IPv6Address\": \"\"\r\n            }\r\n        },\r\n        \"Options\": {\r\n            \"com.docker.network.driver.overlay.vxlanid_list\": \"4102\"\r\n        },\r\n        \"Labels\": {\r\n            \"com.docker.stack.namespace\": \"test\"\r\n        },\r\n        \"Peers\": [\r\n            {\r\n                \"Name\": \"eb787c8b22e8\",\r\n                \"IP\": \"192.168.1.23\"\r\n            }\r\n        ]\r\n    }\r\n]\r\n```\r\n\r\nNote the container addresses should be `10.0.5.3` and `10.0.5.6`, let's check them.\r\n\r\n`docker exec -it test_first.1.qbwe3xsyuiaas50reme2ubtbr sh` and then `ifconfig`:\r\n\r\n```\r\neth0      Link encap:Ethernet  HWaddr 02:42:0A:00:05:03\r\n          inet addr:10.0.5.3  Bcast:10.0.5.255  Mask:255.255.255.0\r\n          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1\r\n          RX packets:0 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:0\r\n          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)\r\n\r\neth1      Link encap:Ethernet  HWaddr 02:42:AC:12:00:03\r\n          inet addr:172.18.0.3  Bcast:172.18.255.255  Mask:255.255.0.0\r\n          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1\r\n          RX packets:188 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:0\r\n          RX bytes:8300 (8.1 KiB)  TX bytes:0 (0.0 B)\r\n\r\nlo        Link encap:Local Loopback\r\n          inet addr:127.0.0.1  Mask:255.0.0.0\r\n          UP LOOPBACK RUNNING  MTU:65536  Metric:1\r\n          RX packets:0 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:1000\r\n          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)\r\n```\r\n\r\n`docker exec -it test_second.1.rermha7mo5sipex53qm6o0s9o sh` and then `ifconfig`:\r\n\r\n```\r\neth0      Link encap:Ethernet  HWaddr 02:42:0A:00:05:06\r\n          inet addr:10.0.5.6  Bcast:10.0.5.255  Mask:255.255.255.0\r\n          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1\r\n          RX packets:1 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:0\r\n          RX bytes:42 (42.0 B)  TX bytes:0 (0.0 B)\r\n\r\neth1      Link encap:Ethernet  HWaddr 02:42:AC:12:00:0A\r\n          inet addr:172.18.0.10  Bcast:172.18.255.255  Mask:255.255.0.0\r\n          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1\r\n          RX packets:355 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:0\r\n          RX bytes:15342 (14.9 KiB)  TX bytes:0 (0.0 B)\r\n\r\nlo        Link encap:Local Loopback\r\n          inet addr:127.0.0.1  Mask:255.0.0.0\r\n          UP LOOPBACK RUNNING  MTU:65536  Metric:1\r\n          RX packets:0 errors:0 dropped:0 overruns:0 frame:0\r\n          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0\r\n          collisions:0 txqueuelen:1000\r\n          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)\r\n```\r\n\r\nSo far, so good, now let's ping by name and nslookup each other:\r\n\r\nOn `first` container `ping second`:\r\n\r\n```\r\nPING second (10.0.5.5): 56 data bytes\r\n64 bytes from 10.0.5.5: seq=0 ttl=64 time=0.184 ms\r\n64 bytes from 10.0.5.5: seq=1 ttl=64 time=0.113 ms\r\n64 bytes from 10.0.5.5: seq=2 ttl=64 time=0.119 ms\r\n^C\r\n--- second ping statistics ---\r\n3 packets transmitted, 3 packets received, 0% packet loss\r\nround-trip min/avg/max = 0.113/0.138/0.184 ms\r\n```\r\n\r\n`nslookup second`:\r\n\r\n```\r\nnslookup: can't resolve '(null)': Name does not resolve\r\n\r\nName:      second\r\nAddress 1: 10.0.5.5\r\n```\r\n\r\nThe other way round, `ping first`:\r\n\r\n```\r\nPING first (10.0.5.2): 56 data bytes\r\n64 bytes from 10.0.5.2: seq=0 ttl=64 time=0.075 ms\r\n64 bytes from 10.0.5.2: seq=1 ttl=64 time=0.060 ms\r\n64 bytes from 10.0.5.2: seq=2 ttl=64 time=0.064 ms\r\n^C\r\n--- first ping statistics ---\r\n3 packets transmitted, 3 packets received, 0% packet loss\r\nround-trip min/avg/max = 0.060/0.066/0.075 ms\r\n```\r\n\r\n`nslookup first`:\r\n\r\n```\r\nnslookup: can't resolve '(null)': Name does not resolve\r\n\r\nName:      first\r\nAddress 1: 10.0.5.2\r\n```\r\n\r\nWhat? Why ping to `10.0.5.2` and `10.0.5.5` works and DNS resolves to them while these addresses aren't even present anywhere? Maybe, some glitch? Let's see.\r\n\r\n`docker stop test_first.1.qbwe3xsyuiaas50reme2ubtbr test_second.1.rermha7mo5sipex53qm6o0s9o` then `docker network inspect test_default` after the service recreates containers:\r\n\r\n```json\r\n[\r\n    {\r\n        \"Name\": \"test_default\",\r\n        \"Id\": \"quisbu0cbrgz9acy9j808hrxu\",\r\n        \"Created\": \"2018-12-18T10:00:10.846072788+07:00\",\r\n        \"Scope\": \"swarm\",\r\n        \"Driver\": \"overlay\",\r\n        \"EnableIPv6\": false,\r\n        \"IPAM\": {\r\n            \"Driver\": \"default\",\r\n            \"Options\": null,\r\n            \"Config\": [\r\n                {\r\n                    \"Subnet\": \"10.0.5.0/24\",\r\n                    \"Gateway\": \"10.0.5.1\"\r\n                }\r\n            ]\r\n        },\r\n        \"Internal\": false,\r\n        \"Attachable\": false,\r\n        \"Ingress\": false,\r\n        \"ConfigFrom\": {\r\n            \"Network\": \"\"\r\n        },\r\n        \"ConfigOnly\": false,\r\n        \"Containers\": {\r\n            \"15875ea4771e581cb63e27f80d97ab52d19d43f967f354e97550af8864d9e798\": {\r\n                \"Name\": \"test_second.1.uzbttwyswm8t0ajt1z9ucmw4l\",\r\n                \"EndpointID\": \"42927351b0b94a1acab1c567a959b5d45b36118031bf12571446bed3d7330820\",\r\n                \"MacAddress\": \"02:42:0a:00:05:07\",\r\n                \"IPv4Address\": \"10.0.5.7/24\",\r\n                \"IPv6Address\": \"\"\r\n            },\r\n            \"3f904b9f904cba634e697a8db04938c77b1d0bf897a86ab2c020515c228fe9f3\": {\r\n                \"Name\": \"test_first.1.ys7ul4vpkcpfjulcx5l11phtl\",\r\n                \"EndpointID\": \"921745cb0d0b5f4e3687792b8fffa14ba088da1ebea1194f76818751bb2b0bde\",\r\n                \"MacAddress\": \"02:42:0a:00:05:08\",\r\n                \"IPv4Address\": \"10.0.5.8/24\",\r\n                \"IPv6Address\": \"\"\r\n            },\r\n            \"lb-test_default\": {\r\n                \"Name\": \"test_default-endpoint\",\r\n                \"EndpointID\": \"90df88a051eaf6557bf22883a6659044826d288f41559728ba5b13d6b5efed36\",\r\n                \"MacAddress\": \"02:42:0a:00:05:04\",\r\n                \"IPv4Address\": \"10.0.5.4/24\",\r\n                \"IPv6Address\": \"\"\r\n            }\r\n        },\r\n        \"Options\": {\r\n            \"com.docker.network.driver.overlay.vxlanid_list\": \"4102\"\r\n        },\r\n        \"Labels\": {\r\n            \"com.docker.stack.namespace\": \"test\"\r\n        },\r\n        \"Peers\": [\r\n            {\r\n                \"Name\": \"eb787c8b22e8\",\r\n                \"IP\": \"192.168.1.23\"\r\n            }\r\n        ]\r\n    }\r\n]\r\n```\r\n\r\nAddresses have changed, that's good. What about DNS?\r\n\r\n`docker exec -it test_first.1.ys7ul4vpkcpfjulcx5l11phtl sh`, then `nslookup second`:\r\n\r\n```\r\nnslookup: can't resolve '(null)': Name does not resolve\r\n\r\nName:      second\r\nAddress 1: 10.0.5.5\r\n```\r\n\r\nThe other way round, `docker exec -it test_second.1.uzbttwyswm8t0ajt1z9ucmw4l sh`, followed by `nslookup first`:\r\n\r\n```\r\nnslookup: can't resolve '(null)': Name does not resolve\r\n\r\nName:      first\r\nAddress 1: 10.0.5.2\r\n```\r\n\r\nNope, same thing. What kind of magic is happening here? NAT? Not a good thing, this breaks everything that checks the once resolved IP address at the application level."}}
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