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Default behavior for port mapping #6958

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nickethier opened this issue Jan 17, 2020 · 3 comments · Fixed by #10828
Closed

Default behavior for port mapping #6958

nickethier opened this issue Jan 17, 2020 · 3 comments · Fixed by #10828
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@tgross
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theme/networking type/enhancement

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@nickethier
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nickethier commented Jan 17, 2020 •
edited by schmichael
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Currently the following network stanza will generate an error:

network {
  mode = "bridge"
  port "http" { }
}

This is because there is no to field in the port stanza. We should change this to map the to field to what ever the host port is assigned. This means for a dynamic port, if to is not specified Nomad will map the port to the same value that is allocated for the dynamic port. For static ports, this means the port will get mapped to the same port specified in static.

This change should be noted in the Version Specific Upgrade notes as its a significant change in behavior.
@nickethier nickethier added this to the unscheduled milestone Jan 17, 2020
@nickethier nickethier mentioned this issue Jan 17, 2020
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@tgross tgross removed this from the unscheduled milestone Feb 12, 2021
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tgross commented Jun 28, 2021

I'm doing some networking documentation cleanup and this issue seems to conflict with #9456 where they're claiming that we already have this. I've verified this with the following jobspec on Nomad 1.1.2:

jobspec 
job "example" {
  datacenters = ["dc1"]

  group "web" {

    network {
      mode = "bridge"
      port "www" {
        // to = 8001
      }
    }

    task "httpd" {
      driver = "docker"

      config {
        image   = "busybox:1"
        command = "httpd"
        args    = ["-v", "-f", "-p", "${NOMAD_PORT_www}", "-h", "/local"]
        ports   = ["www"]
      }

      template {
        data        = "<html>hello, world</html>"
        destination = "local/index.html"
      }

      resources {
        cpu    = 128
        memory = 128
      }
    }
  }
}

Run the job and see that the unspecified port is being mapped to the dynamic port, just as this issue says:

$ nomad job run ./example.nomad
==> 2021-06-28T18:31:49Z: Monitoring evaluation "eb98212a"
    2021-06-28T18:31:49Z: Evaluation triggered by job "example"
    2021-06-28T18:31:49Z: Allocation "0853a728" created: node "1eba2e0c", group "web"
...

$ nomad alloc status 085
ID                  = 0853a728-297d-4e32-9f91-c8758297b38e
...
Allocation Addresses (mode = "bridge")
Label  Dynamic  Address
*www   yes      10.0.2.15:20158
...

$ curl 10.0.2.15:20158
<html>hello, world</html>

So it sounds like the way we could close out both #6958 and #9456 is to change the port map to documentation as follows:

diff --git a/website/content/docs/job-specification/network.mdx b/website/content/docs/job-specification/network.mdx
index 02f688830..7d1a1ceb0 100644
--- a/website/content/docs/job-specification/network.mdx
+++ b/website/content/docs/job-specification/network.mdx
@@ -72,9 +72,10 @@ job "docs" {
   dynamic port is chosen. We **do not recommend** using static ports, except
   for `system` or specialized jobs like load balancers.
 - `to` `(string:nil)` - Applicable when using "bridge" mode to configure port
-  to map to inside the task's network namespace. `-1` sets the mapped port equal to the
-  dynamic port allocated by the scheduler. The `NOMAD_PORT_<label>` environment variable
-  will contain the `to` value.
+  to map to inside the task's network namespace. Omitting this field or
+  setting it to `-1` sets the mapped port equal to the dynamic port allocated
+  by the scheduler. The `NOMAD_PORT_<label>` environment variable will contain
+  the `to` value.
 - `host_network` `(string:nil)` - Designates the host network name to use when allocating
   the port. When port mapping the host port will only forward traffic to the matched host
   network address.

@tgross
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tgross commented Jun 28, 2021

I found the PR where this got done originally, which was a side-effect of #8208. I'll make a PRs and changelog PR to call it out to close both this and #9456

This was referenced Jun 28, 2021
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@tgross tgross self-assigned this Jun 28, 2021
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docs: unset port to field maps to dynamic port hashicorp/nomad
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