The Problem & The Question
I'm trying to create an AWS ElastiCache Redis-flavored cluster and connect to it from an instance in the same VPC. When I create the cluster initially, I can connect to it just fine via redis-cli. If I wait a day or two and then try to connect to it again via redis-cli, I get the following error:
$ redis-cli -h <aws-elasticache-cluster-primary-endpoint>
Could not connect to Redis at <aws-elasticache-cluster-primary-endpoint>:6379: Name or service not known
not connected>
I should be able to connect again with no issue. Why would I be getting DNS errors the next day when it worked initially? Nothing has changed about the cluster since I created it. How could I fix this?
Steps to Reproduce
ElastiCache Dashboard -> Redis -> Create.
Set the following options:
Option Value Cluster Engine Redis Location Amazon Cloud Engine version compatibility 6.x Port 6379 Parameter group default.redis6.x Node type cache.t3.micro Number of replicas 0 Multi-AZ false Subnet group default Security groups default Encryption at-rest false Encryption in-transit false Create.
After creating, verify you can connect to the cluster with:
redis-cli -h <aws-elasticache-cluster-primary-endpoint>Disconnect.
Try reconnecting with the same
redis-clicommand a few days later. You should see the errors shown in the section above.
Additional Information
nping
$ sudo nping --tcp -p 6379 <aws-elasticache-cluster-primary-endpoint>
Failed to resolve given hostname/IP: <aws-elasticache-cluster-primary-endpoint>. Note that you can't use '/mask' AND '1-4,7,100-' style IP ranges
Cannot find a valid target. Please make sure the specified hosts are either IP addresses in standard notation or hostnames that can be resolved with DNS
nslookup
$ sudo nslookup <aws-elasticache-cluster-primary-endpoint>
Server: 75.75.75.75
Address: 75.75.75.75#53
** server can't find <aws-elasticache-cluster-primary-endpoint>: REFUSED
Reachability Analyzer
I followed AWS' instructions for testing connectivity from my EC2 instance to the ElastiCache cluster. The results I got back for the connectivity were:
| Reachability Status | State |
|---|---|
| Reachable | Succeeded |
Cluster Metrics
| Metric | Value |
|---|---|
| CPU Utilization | ~1.000% |
| Engine CPU Utilization | ~0.283% |
| Database Memory Usage Percentage | ~1.093% |
Local Wireguard configuration
[Interface]
PrivateKey = <value>
ListenPort = 21841
Address = 10.0.0.2/32
DNS = 9.9.9.9 # 75.75.75.75 75.75.76.76
[Peer]
PublicKey = <value>
AllowedIPs = 0.0.0.0/0, ::/0
Endpoint = <public-IP>:51820
