tensorflow saved_model, `tags` is the `key` to the metagraph

tf_serve_understanding.py

import tensorflow as tf
import numpy as np

# graph
tf.reset_default_graph()
x = tf.placeholder(tf.float32, [], name='x')
y = tf.multiply(x, 2, name='y')
z = tf.add(x, 1, name='z')

# signature
model_inputs = tf.saved_model.utils.build_tensor_info(x)
model_outputs_y = tf.saved_model.utils.build_tensor_info(y)
model_outputs_z = tf.saved_model.utils.build_tensor_info(z)

model_xy_sig = tf.saved_model.signature_def_utils.build_signature_def(
    inputs={
        'x':
        model_inputs
    }, 
    outputs={
        'y':
        model_outputs_y
    }, 
    method_name='xy')

model_xz_sig = tf.saved_model.signature_def_utils.build_signature_def(
    inputs={
        'x':
        model_inputs
    }, 
    outputs={
        'z':
        model_outputs_z
    }, 
    method_name='xz')
    
# export
EXPORT_DIR = './exported_model'
if tf.gfile.Exists(EXPORT_DIR):
    tf.gfile.DeleteRecursively(EXPORT_DIR)
builder = tf.saved_model.builder.SavedModelBuilder(EXPORT_DIR)

with tf.Session() as sess:
    builder.add_meta_graph_and_variables(
        sess,
        tags=[tf.saved_model.tag_constants.SERVING, 'xy', 'xz'],
        signature_def_map={
            'signature-xy': model_xy_sig,
#             'signature-xz': model_xz_sig
        }
    )
#     builder.add_meta_graph(
#         sess,
#         tags=[tf.saved_model.tag_constants.SERVING, 'xz'],
#         signature_def_map={
#             'signature-xz': model_xz_sig
#         }
#     )
    
builder.save()

# load
tf.reset_default_graph()
with tf.Session() as sess:
    gd = tf.saved_model.loader.load(sess, [tf.saved_model.tag_constants.SERVING, 'xy', 'xz'], EXPORT_DIR)
#     tf.saved_model.loader.load(sess, ['xt', tf.saved_model.tag_constants.SERVING, 'xz'], EXPORT_DIR)
    g = tf.get_default_graph()
    print(g.get_operations())
    x = g.get_tensor_by_name('x:0')
    y = g.get_tensor_by_name('y:0')
    z = g.get_tensor_by_name('z:0')
    print(sess.run([y, z], feed_dict={x: 100}))
    
# check loaded graph definition
sig1 = gd.signature_def['signature-xy']
sig1.inputs
sig1.outputs