As a DevOps engineer, it's essential to have a solid understanding of default port numbers used in various technologies. Here are some key ones you should be familiar with:

* HTTP: 80
* HTTPS: 443
* SSH: 22
* RDP: 3389
* FTP: 21
* SFTP: 22
* Telnet: 23
* SMTP: 25
* DNS: 53
* NFS: 2048, 2049, 111

For CI/CD tools:
* Jenkins: 8080 (default), 8443 (HTTPS)
* GitLab CI: 80 (HTTP), 443 (HTTPS)

For SonarQube:
* 9000

For Artifact Repositories:
* Nexus Repository: 8081 (default for HTTP)
* JFrog Artifactory: 8081 (for HTTP) and 443 (for HTTPS)

For Containerization and Orchestration:
* Docker: 2375 (HTTP), 2376 (HTTPS)
* Kubernetes: 6443, 10250, 10256
* Etcd: 2379 (client) and 2380 (peer)

For Monitoring and Logging:
* Prometheus: 9090
* Grafana: 3000
* ELK Stack (Elasticsearch, Logstash, Kibana): Elasticsearch - 9200 (HTTP), 9300 (Transport); Logstash - 5044 (Beats), 5000 (TCP/UDP); Kibana - 5601; Splunk: 8089
* Kiali: Default port 20001
* Jaeger: Jaeger UI - 16686; Jaeger Collector - 14268; Jaeger Agent - 5775 (UDP)

Source: https://dev.to/jeyasurya2201/some-key-default-port-numbers-that-a-devops-engineer-should-be-familiar-with-4j5c