what ports Jenkins uses when it's on the docker?

Question

I have a Jenkins docker container running on a ubuntu 20.04 machine.
I have a job on my Jenkins which polls a GitLab repository and uses MVN to deploy it on a Nexus server.
What I want to do is to close all ports in my server so I can reduce the risk of being hacked but I don't know which ports should I leave open apart from 8080 and 50000.
Jenkins: jenkins/jenkins:2.361.1-lts-jdk11
Shell Scripts that jenkins executes:

export MAVEN_HOME=/var/apache-maven-3.8.6
export PATH=$PATH:$MAVEN_HOME/bin
cd myproject
mvn clean package deploy

Thank you in advance.

Answer 1

If you want to check what ports are exposed in the Docker image, you can simply use the docker inspect command.

docker inspect jenkins/jenkins:2.361.1-lts-jdk11

The above command will return the following, here you just search for ExposedPorts.

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        "Id": "sha256:729c87ece8d086b05a3a67e1f7b7a7e669c3a50db75ea2440dd6099a3f887111",
        "RepoTags": [
            "jenkins/jenkins:2.361.1-lts-jdk11"
        ],
        "RepoDigests": [
            "jenkins/jenkins@sha256:5508cb1317aa0ede06cb34767fb1ab3860d1307109ade577d5df871f62170214"
        ],
        "Parent": "",
        "Comment": "buildkit.dockerfile.v0",
        "Created": "2022-09-07T12:02:24.712441461Z",
        "Container": "",
        "ContainerConfig": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
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            "AttachStderr": false,
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            "OpenStdin": false,
            "StdinOnce": false,
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            "Cmd": null,
            "Image": "",
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": null
        },
        "DockerVersion": "",
        "Author": "",
        "Config": {
            "Hostname": "",
            "Domainname": "",
            "User": "jenkins",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "50000/tcp": {},
                "8080/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/opt/java/openjdk/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "LANG=C.UTF-8",
                "JENKINS_HOME=/var/jenkins_home",
                "JENKINS_SLAVE_AGENT_PORT=50000",
                "REF=/usr/share/jenkins/ref",
                "JENKINS_VERSION=2.361.1",
                "JENKINS_UC=https://updates.jenkins.io",
                "JENKINS_UC_EXPERIMENTAL=https://updates.jenkins.io/experimental",
                "JENKINS_INCREMENTALS_REPO_MIRROR=https://repo.jenkins-ci.org/incrementals",
                "COPY_REFERENCE_FILE_LOG=/var/jenkins_home/copy_reference_file.log",
                "JAVA_HOME=/opt/java/openjdk"
            ],
            "Cmd": null,
            "Image": "",
            "Volumes": {
                "/var/jenkins_home": {}
            },
            "WorkingDir": "",
            "Entrypoint": [
                "/usr/bin/tini",
                "--",
                "/usr/local/bin/jenkins.sh"
            ],
            "OnBuild": null,
            "Labels": {
                "org.opencontainers.image.description": "The Jenkins Continuous Integration and Delivery server",
                "org.opencontainers.image.licenses": "MIT",
                "org.opencontainers.image.revision": "00d1edcbf6e0bd78ff5b359731310b91bdac9b07",
                "org.opencontainers.image.source": "https://github.com/jenkinsci/docker",
                "org.opencontainers.image.title": "Official Jenkins Docker image",
                "org.opencontainers.image.url": "https://www.jenkins.io/",
                "org.opencontainers.image.vendor": "Jenkins project",
                "org.opencontainers.image.version": "2.361.1"
            }
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 463047412,
        "VirtualSize": 463047412,
        "GraphDriver": {
            "Data": {
                "LowerDir": "/var/lib/docker/overlay2/b87f7dbd3ccb73d1d498c6c4776983a4a9987ed321a7879bbba8f1fc6b24c349/diff:/var/lib/docker/overlay2/dbe3badbc23d551bc9c75baf27268489a6aad4b20430ac97ef2e1aad55a8fc07/diff:/var/lib/docker/overlay2/ae3db8be1ef114178bafc0054933f73dcc2672f9dd1fe4a86a1391a5669ee0ed/diff:/var/lib/docker/overlay2/963904c7b1cd906120b6dc3fbefcbf954735d95cdbc81358909ca0ad891a996b/diff:/var/lib/docker/overlay2/da6f957a0563ce381dece995353e75e3bc94ad048892dcfa831f8a2e41528815/diff:/var/lib/docker/overlay2/7a963ecdeabc85980fbc61bc401818a58572eb3856885542ab9b3ecd7e3f2205/diff:/var/lib/docker/overlay2/9024a41086f6c2fa44bafc813dcbcebd01c83124a7da1e245d5b274b33aa43ff/diff:/var/lib/docker/overlay2/e2ee20b24525e750dc228ea17e3ac7debab0db6b11a4a113bec7737b9e4cd1af/diff:/var/lib/docker/overlay2/9ac2fb80407369d732fce5756bc6f7509874ae8072a5b368bc396757978f0773/diff:/var/lib/docker/overlay2/16c96992e082851b7745a3697da020f7ff7b2c0b11a85bbcff577a5c0018d6a1/diff:/var/lib/docker/overlay2/90477c9091098ece50aa59df3c6965984c3db0ad92f41817fb2cb6d410f68d5e/diff:/var/lib/docker/overlay2/953b244f3ee262704ce382a6edc573e4d0c2713c3311448bbc5fd6799a3217a1/diff:/var/lib/docker/overlay2/98b91e296c5b64b6d46d07e5e3f2a1ce93df7eb475d679a7e7c6c5ee34e05848/diff",
                "MergedDir": "/var/lib/docker/overlay2/f4c663aa276a1d387f6d6b83d2bdb8b930d611eb1b0908b7968af790b1953b93/merged",
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                "WorkDir": "/var/lib/docker/overlay2/f4c663aa276a1d387f6d6b83d2bdb8b930d611eb1b0908b7968af790b1953b93/work"
            },
            "Name": "overlay2"
        },
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