Example redirect migration from XML source in Drupal 8.

migrate_plus.migration.redirects.yml

id: redirects
label: Old article paths.
migration_group: content
source:
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: simple_xml
  urls: http://kevinquillen.com/atom.xml
  namespaces:
    atom: http://www.w3.org/2005/Atom
  item_selector: //atom:entry
  fields:
    -
      name: slug
      label: 'ID'
      selector: atom:id
  ids:
    slug:
      type: string
  constants:
    redirect_prefix: 'internal:/node/'
    uid: 1
    status: 301
destination:
  plugin: 'entity:redirect'
process:
  node:
    plugin: migration_lookup
    source: slug
    migration: article
  redirect_source:
    - plugin: str_replace
      source: slug
      search: 'http://kevinquillen.com/'
      replace: ''
  redirect_redirect:
    plugin: concat
    source:
      - constants/redirect_prefix
      - "@node"
  uid: constants/uid
  status_code: constants/status
dependencies:
  enforced:
    module:
      - kevinquillen_migration
migration_dependencies:
  required:
    - article