Docker port mapping gets ignored

Question

I created an image with Asp.Net. The Dockerfile looks like

FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["AspMini/AspMini.csproj", "AspMini/"]
RUN dotnet restore "AspMini/AspMini.csproj"
COPY . .
WORKDIR "/src/AspMini"
RUN dotnet build "AspMini.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "AspMini.csproj" -c Release -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "AspMini.dll"]

However if i start a container with

docker run theImageName -d -p 8090:80

the mapping gets ignored. I can't access the api on localhost:8090.

The docker inspect output: docker inspect 991f8f09c1a6

[
    {
        "Id": "991f8f09c1a618ad05ca3910f9f570c15217f6753ce0fbb07203de21df66310a",
        "Created": "2023-01-13T14:42:03.686922616Z",
        "Path": "dotnet",
        "Args": [
            "AspMini.dll",
            "-d",
            "-p",
            "8090:80"
        ],
        "State": {
            "Status": "running",
            "Running": true,
            "Paused": false,
            "Restarting": false,
            "OOMKilled": false,
            "Dead": false,
            "Pid": 1748,
            "ExitCode": 0,
            "Error": "",
            "StartedAt": "2023-01-13T14:42:04.089973705Z",
            "FinishedAt": "0001-01-01T00:00:00Z"
        },

        "Name": "/beautiful_gagarin",
        "RestartCount": 0,
        "Driver": "overlay2",
        "Platform": "linux",
        "MountLabel": "",
        "ProcessLabel": "",
        "AppArmorProfile": "",
        "ExecIDs": null,
        "HostConfig": {
            "Binds": null,
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "json-file",
                "Config": {}
            },
            "NetworkMode": "default",
            "PortBindings": {},
            "RestartPolicy": {
                "Name": "no",
                "MaximumRetryCount": 0
            },
            "AutoRemove": false,
            "VolumeDriver": "",
            "VolumesFrom": null,
            "CapAdd": null,
            "CapDrop": null,
            "CgroupnsMode": "host",
            "Dns": [],
            "DnsOptions": [],
            "DnsSearch": [],
            "ExtraHosts": null,
            "GroupAdd": null,
            "IpcMode": "private",
            "Cgroup": "",
            "Links": null,
            "OomScoreAdj": 0,
            "PidMode": "",
            "Privileged": false,
            "PublishAllPorts": false,
            "ReadonlyRootfs": false,
            "SecurityOpt": null,
            "UTSMode": "",
            "UsernsMode": "",
            "ShmSize": 67108864,
            "Runtime": "runc",
            "ConsoleSize": [
                35,
                161
            ],
            "Isolation": "",
            "CpuShares": 0,
            "Memory": 0,
            "NanoCpus": 0,
            "CgroupParent": "",
            "BlkioWeight": 0,
            "BlkioWeightDevice": [],
            "BlkioDeviceReadBps": null,
            "BlkioDeviceWriteBps": null,
            "BlkioDeviceReadIOps": null,
            "BlkioDeviceWriteIOps": null,
            "CpuPeriod": 0,
            "CpuQuota": 0,
            "CpuRealtimePeriod": 0,
            "CpuRealtimeRuntime": 0,
            "CpusetCpus": "",
            "CpusetMems": "",
            "Devices": [],
            "DeviceCgroupRules": null,
            "DeviceRequests": null,
            "KernelMemory": 0,
            "KernelMemoryTCP": 0,
            "MemoryReservation": 0,
            "MemorySwap": 0,
            "MemorySwappiness": null,
            "OomKillDisable": false,
            "PidsLimit": null,
            "Ulimits": null,
            "CpuCount": 0,
            "CpuPercent": 0,
            "IOMaximumIOps": 0,
            "IOMaximumBandwidth": 0,
            "MaskedPaths": [
                "/proc/asound",
                "/proc/acpi",
                "/proc/kcore",
                "/proc/keys",
                "/proc/latency_stats",
                "/proc/timer_list",
                "/proc/timer_stats",
                "/proc/sched_debug",
                "/proc/scsi",
                "/sys/firmware"
            ],
            "ReadonlyPaths": [
                "/proc/bus",
                "/proc/fs",
                "/proc/irq",
                "/proc/sys",
                "/proc/sysrq-trigger"
            ]
        },
        "GraphDriver": {
            "Data": {
                "LowerDir": "/var/lib/docker/overlay2/9c973e90ec99d50f84e8ee2747fa4646d5f8599a2f03646ac5301418cb542a88-init/diff:/var/lib/docker/overlay2/603fdf539efa645bb21ef84b7b3f6c0d833fbd03faad8dffd5defa4b68bbb42b/diff:/var/lib/docker/overlay2/7ba1ebf47509f54abc170cf2a0d57e03513c7ed94f05f6b836abaacf9a304c18/diff:/var/lib/docker/overlay2/87a8e5b62cb7841e224f121dac133fc1de10c7e11a71d908da9991423cab318d/diff:/var/lib/docker/overlay2/ac3471c9a4388af7f1a556b6796a6d7eb640d6831983b3ff7cc9c41361d674e8/diff:/var/lib/docker/overlay2/03d18c531853da913373bae78ddba3986d90705862c1ac84a49d9ec8ba9ce9c5/diff:/var/lib/docker/overlay2/d179824e5cc7707e84a46192e2c5d93d297828703c555747395a8173034152e6/diff:/var/lib/docker/overlay2/bbb62ce4f5330dca608c3d7ce8ef9e621d12bbae16a1634b23950033e629afa3/diff",
                "MergedDir": "/var/lib/docker/overlay2/9c973e90ec99d50f84e8ee2747fa4646d5f8599a2f03646ac5301418cb542a88/merged",
                "UpperDir": "/var/lib/docker/overlay2/9c973e90ec99d50f84e8ee2747fa4646d5f8599a2f03646ac5301418cb542a88/diff",
                "WorkDir": "/var/lib/docker/overlay2/9c973e90ec99d50f84e8ee2747fa4646d5f8599a2f03646ac5301418cb542a88/work"
            },
            "Name": "overlay2"
        },
        "Mounts": [],
        "Config": {
            "Hostname": "991f8f09c1a6",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": true,
            "AttachStderr": true,
            "ExposedPorts": {
                "80/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "ASPNETCORE_URLS=http://+:80",
                "DOTNET_RUNNING_IN_CONTAINER=true",
                "DOTNET_VERSION=6.0.13",
                "ASPNET_VERSION=6.0.13"
            ],
            "Cmd": [
                "-d",
                "-p",
                "8090:80"
            ],
            "Image": "aspmini",
            "Volumes": null,
            "WorkingDir": "/app",
            "Entrypoint": [
                "dotnet",
                "AspMini.dll"
            ],
            "OnBuild": null,
            "Labels": {}
        },
        "NetworkSettings": {
            "Bridge": "",
            "SandboxID": "5a2a584a1c775babb79a9a1434d3762c8511f1ac124084cde9147a3427ef2c73",
            "HairpinMode": false,
            "LinkLocalIPv6Address": "",
            "LinkLocalIPv6PrefixLen": 0,
            "Ports": {
                "80/tcp": null
            },
            "SandboxKey": "/var/run/docker/netns/5a2a584a1c77",
            "SecondaryIPAddresses": null,
            "SecondaryIPv6Addresses": null,
            "EndpointID": "9618ce41bddab811bcecbf107db63fde2153f60ca8926f48ac4e6610edc89749",
            "Gateway": "172.17.0.1",
            "GlobalIPv6Address": "",
            "GlobalIPv6PrefixLen": 0,
            "IPAddress": "172.17.0.3",
            "IPPrefixLen": 16,
            "IPv6Gateway": "",
            "MacAddress": "02:42:ac:11:00:03",
            "Networks": {
                "bridge": {
                    "IPAMConfig": null,
                    "Links": null,
                    "Aliases": null,
                    "NetworkID": "75751644df6485eacd29cb213ee4ab2bee73f1214b9e99371406df1df39591d8",
                    "EndpointID": "9618ce41bddab811bcecbf107db63fde2153f60ca8926f48ac4e6610edc89749",
                    "Gateway": "172.17.0.1",
                    "IPAddress": "172.17.0.3",
                    "IPPrefixLen": 16,
                    "IPv6Gateway": "",
                    "GlobalIPv6Address": "",
                    "GlobalIPv6PrefixLen": 0,
                    "MacAddress": "02:42:ac:11:00:03",
                    "DriverOpts": null
                }
            }
        }
    }
]

PortBindings is just empty. But if i start the Container over the GUI:

it works. Why is the -p flag ignored?

Answer 1

On the docker run command, parameters in front of the image name are Docker parameters and parameters after the image name are for the program running in the image.

-p and -d are for Docker, so they need to go in front of the image name, like this

docker run -d -p 8090:80 theImageName