Use GitLab CI to upload built Go binaries to a Nexus (raw) repository. Don't forget to define the four "UPLOAD_NEXUS_..." environment variables in the CI configuration

.gitlab-ci.yml

variables:
  BIN_NAME: executable-name
  ARTIFACTS_DIR: build
  GO_PROJECT: example.com/go/project/module/path
  GOFLAGS: -mod=readonly
  GOPRIVATE: example.com/go/if/needed
  GOBIN: ${CI_PROJECT_DIR}/bin

# Use this to install any binary tools needed
# and to create the output directory
before_script:
  - export PATH=${GOBIN}:${PATH}
  - go install github.com/kevinburke/go-bindata/go-bindata
  - mkdir -p ${CI_PROJECT_DIR}/${ARTIFACTS_DIR}

build:
  script:
    - go generate ./...
    - go build --tags release -i -v -o ${CI_PROJECT_DIR}/${ARTIFACTS_DIR}/${BIN_NAME}
    - go run scripts/upload-to-nexus.go
  artifacts:
    paths:
      - ${ARTIFACTS_DIR}

upload-to-nexus.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"time"
)

func main() {
	base, n := getenv("UPLOAD_NEXUS_BASE", 0)
	repo, n := getenv("UPLOAD_NEXUS_REPO", n)
	user, n := getenv("UPLOAD_NEXUS_USER", n)
	pass, n := getenv("UPLOAD_NEXUS_PASS", n)
	binName, n := getenv("BIN_NAME", n)
	ciProjectDir, n := getenv("CI_PROJECT_DIR", n)
	artifactsDir, n := getenv("ARTIFACTS_DIR", n)

	if n != 7 {
		fmt.Println("Missing one or more envvars UPLOAD_NEXUS_*")
		os.Exit(1)
	}

	subfolder := "UNKNOWN"

	if tagName, ok := os.LookupEnv("CI_COMMIT_TAG") {
		subfolder = tagName
	} else {
		currentTime := time.Now().Format("20060102")
		subfolder += "-" + currentTime
		if hash, ok := os.LookupEnv("CI_COMMIT_SHORT_SHA"); ok {
			subfolder += "-" + hash
		}
	}

	url := fmt.Sprintf("%s/repository/%s/%s/%s/%s", base, repo, binName, subfolder, binName)
	filePath := fmt.Sprintf("%s/%s/%s", ciProjectDir, artifactsDir, binName)

	fmt.Printf("Uploading from %s\n", filePath)
	fmt.Printf("Uploading to   %s\n", url)

	uploadFile(url, filePath, user, pass)
}

func getenv(name string, number int) (string, int) {
	if value, ok := os.LookupEnv(name); ok {
		return value, number + 1
	}

	return "", number
}

func uploadFile(url string, filepath string, user string, pass string) {
	f, err := os.Open(filepath)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

	req, err := http.NewRequest(http.MethodPut, url, f)
	if err != nil {
		log.Fatal(err)
	}

	req.SetBasicAuth(user, pass)

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		log.Fatal(err)
	}

	defer resp.Body.Close()

	content, err := ioutil.ReadAll(resp.Body)

	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(string(content))
}