问题
I have created two replicas (replica set name = rs0) of mongodb with a headless service.
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: tickets-mongo-depl
spec:
replicas: 2
serviceName: tickets-mongo-srv
selector:
matchLabels:
app: tickets-mongo
template:
metadata:
labels:
app: tickets-mongo
spec:
containers:
- name: tickets-mongo
image: mongo
command:
- mongod
- '--bind_ip_all'
- '--replSet'
- rs0
---
apiVersion: v1
kind: Service
metadata:
name: tickets-mongo-srv
spec:
clusterIP: None
selector:
app: tickets-mongo
ports:
- name: tickets-db
protocol: TCP
port: 27017
targetPort: 27017
pods and the service are working as expected
pod/tickets-mongo-depl-0 1/1 Running 0 50m
pod/tickets-mongo-depl-1 1/1 Running 0 50m
service/tickets-mongo-srv ClusterIP None <none> 27017/TCP 6d12h
I have run the below command to expose the headless service so that i can connect to my database using mongodb compass GUI
kubectl port-forward service/tickets-mongo-srv 7000:27017
Forwarding from 127.0.0.1:7000 -> 27017
Forwarding from [::1]:7000 -> 2701
replica set already initialised.
{
"set" : "rs0",
"date" : ISODate("2020-06-20T08:03:02.019Z"),
"myState" : 1,
"term" : NumberLong(1),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"heartbeatIntervalMillis" : NumberLong(2000),
"majorityVoteCount" : 2,
"writeMajorityCount" : 2,
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"lastCommittedWallTime" : ISODate("2020-06-20T08:02:58.983Z"),
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"readConcernMajorityWallTime" : ISODate("2020-06-20T08:02:58.983Z"),
"appliedOpTime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"durableOpTime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"lastAppliedWallTime" : ISODate("2020-06-20T08:02:58.983Z"),
"lastDurableWallTime" : ISODate("2020-06-20T08:02:58.983Z")
},
"lastStableRecoveryTimestamp" : Timestamp(1592640168, 1),
"lastStableCheckpointTimestamp" : Timestamp(1592640168, 1),
"electionCandidateMetrics" : {
"lastElectionReason" : "electionTimeout",
"lastElectionDate" : ISODate("2020-06-20T06:29:48.607Z"),
"electionTerm" : NumberLong(1),
"lastCommittedOpTimeAtElection" : {
"ts" : Timestamp(0, 0),
"t" : NumberLong(-1)
},
"lastSeenOpTimeAtElection" : {
"ts" : Timestamp(1592634577, 1),
"t" : NumberLong(-1)
},
"numVotesNeeded" : 2,
"priorityAtElection" : 1,
"electionTimeoutMillis" : NumberLong(10000),
"numCatchUpOps" : NumberLong(0),
"newTermStartDate" : ISODate("2020-06-20T06:29:48.634Z"),
"wMajorityWriteAvailabilityDate" : ISODate("2020-06-20T06:29:50.053Z")
},
"members" : [
{
"_id" : 0,
"name" : "tickets-mongo-depl-0.tickets-mongo-srv:27017",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 5750,
"optime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2020-06-20T08:02:58Z"),
"syncingTo" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1592634588, 1),
"electionDate" : ISODate("2020-06-20T06:29:48Z"),
"configVersion" : 1,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 1,
"name" : "tickets-mongo-depl-1.tickets-mongo-srv:27017",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 5604,
"optime" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1592640178, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2020-06-20T08:02:58Z"),
"optimeDurableDate" : ISODate("2020-06-20T08:02:58Z"),
"lastHeartbeat" : ISODate("2020-06-20T08:03:00.524Z"),
"lastHeartbeatRecv" : ISODate("2020-06-20T08:03:00.028Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncingTo" : "tickets-mongo-depl-0.tickets-mongo-srv:27017",
"syncSourceHost" : "tickets-mongo-depl-0.tickets-mongo-srv:27017",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 1
}
],
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1592640178, 1),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1592640178, 1)
}
As you can see in the last image the GUI is trying connect without luck.
Does any of you have any idea why this is??
回答1:
When connecting to a replica set, the hostnames and IP addresses in the connection string are the seed list. The driver will attempt to connect to each host in the seed list in turn, and once it gets a connection will run isMaster.
The isMaster command will return the list of member hostname:port in the replica set, as entered in the configuration document. The client then drops the original connection, and connects to the discovered nodes.
In your case, the following happens:
- Compass connects to localhost:7000, which Kubernetes forwards to port 27017
- The connection is established, Compass runs the
isMastercommand - The node responds with the member list:
o "tickets-mongo-depl-0.tickets-mongo-srv:27017"
o "tickets-mongo-depl-1.tickets-mongo-srv:27017" - Compass attempts to connect to the hostnames provided, but DNS resolution of the name fails
Take a look at the MongoDB documentation on deplying a replica set using Kubernetes
来源：https://stackoverflow.com/questions/62482913/connecting-to-a-mongodb-replicaset-inside-kubernetes-with-mongodb-compass-gui