How do I migrate from Dep to Go Modules

Migrating from Dep to Go Modules is very easy.

1. Run go version and make sure you're using Go version 1.11 or later.
2. Move your code outside of GOPATH or set export GO111MODULE=on.
3. go mod init [module path]: This will import dependencies from Gopkg.lock.
4. go mod tidy: This will remove unnecessary imports, and add indirect ones.
5. (Optional) Delete your vendor folder (rm -rf vendor/ or move to trash)
6. go build: Do a test build to see if it works.
7. rm -f Gopkg.lock Gopkg.toml: Delete the obsolete files used for Dep.

Go has imported my dependencies from Dep by reading the Gopkg.lock file and also created a go.mod file.

If you want to keep your vendor folder:

7. Run go mod vendor to copy your dependencies into the vendor folder.
8. Run go build -mod=vendor to ensure go build uses your vendor folder.

To add to @Nicholas answer's:

Here is from the offical golang documenation:

To create a go.mod for an existing project:

1. Navigate to the root of the module's source tree outside of GOPATH:

$ export GO111MODULE=on                         # manually active module mode
$ cd $GOPATH/src/<project path>                 # e.g., cd $GOPATH/src/you/hello

2. Create the initial module definition and write it to the go.mod file:

$ go mod init      

This step converts from any existing dep Gopkg.lock file or from any of the other nine total supported dependency formats, adding require statements to match the existing configuration.

3. Build the module. When executed from the root directory of a module, the ./... pattern matches all the packages within the current module. go build will automatically add missing or unconverted dependencies as needed to satisfy imports for this particular build invocation:

$ go build ./...

4. Test the module as configured to ensure that it works with the selected versions:

$ go test ./...

5. (Optional) Run the tests for your module plus the tests for all direct and indirect dependencies to check for incompatibilities:

$ go test all