Since the host is already defined in the request, you should not ask for it again in the header.

require 'escher'
require 'net/http'

client = { api_key_id: 'developer', api_secret: 'MzhKUxb2vlHGfJgAMEaVIWyk5BBFilrg' }

request = {
method: 'GET',
host: 'suite.ett.local',
uri: 'api/v2/internal',
body: 'payload',
headers: [['Content-Type', 'application/json']]
}

escher = Escher::Auth.new('eu/suite/ems_request')
escher.sign!(request, client)

.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/escher-0.3.2/lib/escher/auth.rb:23:in sign!': Missing header: Host (Escher::EscherError) from client.rb:15:in