Elixir is great, so clearly we'll all rewrite our applications in Elixir. Mostly, you can't and shouldn't do that. This presentation will show you another path. You’ll see how at Liefery, we started with small steps instead of rewriting everything. This allowed us to reap the benefits earlier and get comfortable before getting deeper into it. We’ll examine in detail the tactics we used to create two Elixir apps for new requirements, and how we integrated them with our existing Rails code base. Join us on our tale of adopting Elixir and Phoenix and see what we learned, what we loved, and what bumps we hit along the road

1. Who wants to go and
build a system in Elixir?

5. Can't go out and
rewrite it all

6. You shouldn’t

7. Elixir, your Monolith and You
(alpha-1)
Tobias Pfeiffer
@PragTob
pragtob.info

8. Your Monolith and You

10. Your Monolith now?

11. Your Monolith?

12. Tear it all down and
rewrite it

14. Sooooon!

15. “We rewrote it all in
Language x, now it’s 10
times faster and only
50% of the code!”
Someone

16. “Language x, is 10 times
faster and requires 50% of
the code of language Y!”
Someone
Often implies...

17. What nobody tells you...

18. Business Value?

19. Sooooon!

20. Replace it step by step

21. We have a bedroom,
for the bathroom please
check out legacy!

22. Terraform allows you to
incrementally transform an
older API into one powered by
Phoenix - one endpoint at a
time.
poteto/terraform

23. defmodule MyApp.Terraformers.Foo do
alias MyApp.Clients.Foo
use Plug.Router
plug :match
plug :dispatch
get "/v1/hello-world", do: send_resp(conn, 200, "Hi")
get _ do
res = Foo.get!(conn)
send_response({:ok, conn, res})
end
end
poteto/terraform

24. Replace a critical
component

25. Check out our sweet new
heating system!

26. Write a new component

27. Check it out we built a
brand new high tech
entertainment facility!

28. Write a new component
Obvious in microservices

29. “Is the technology I’m
choosing the right fit for
the problem I’m trying to
solve?”
Everyone, hopefully

30. Reasonably separate and
limited problem

31. Requirement that poses a
problem for the current
stack

32. Spark of Enthusiasm

33. Courier Tracking

34. Courier Tracking

35. Courier Tracking

36. Courier Tracking
Websockets

37. Courier Tracking
Websockets
Basic Knowledge

38. How to make them talk?

39. Monolith
FrontendCourier
DB

40. MonolithTracking
FrontendCourier
DB DB

41. Connect them?

42. MonolithTracking
FrontendCourier
DB DB

43. JSON
Web
Token

44. Header
Payload
Signature

45. {
"role": "admin",
"courier_ids": [1337, 55],
"id": 42,
"exp": 1520469475
}

46. MonolithTracking
FrontendCourier
DB DB
Shared Secret

47. MonolithTracking
FrontendCourier
DB DB
JWT
JWT
Shared Secret

48. MonolithTracking
FrontendCourier
DB DB
JWTJWT
JWT
Shared Secret
JWT

49. def connect(%{"token" => token}, socket) do
token
|> JWT.verify_token
|> respond_based_on_token_contents(socket)
end
Socket

50. defp login_user(%{"role" => role, ...}, socket) do
{:ok, assign(socket, :user, %{role: role, ...})}
end
Socket

51. def join("courier:" <> courier_id, _, %
{assigns: %{user: user}}) do
if authorized?(courier_id, user) do
# login
else
# unauthorizd
end
end
Channel

52. defp authorized?("", _), do: false
defp authorized?(courier_id, %{courier_ids: ids}) do
Enum.member?(ids, String.to_integer(courier_id))
end
defp authorized?(_, _), do: false
Channel

53. MonolithTracking
FrontendCourier
DB DB
LocationsLocations
Most of the time

54. Fulfillment

55. Fulfillment
CRUD

56. Fulfillment
CRUD
Experience

57. MonolithFulfillment
DB DB

58. MonolithFulfillment
DB DB
Own UI

59. MonolithFulfillment
DB DB
OAuth
OAuth

60. MonolithFulfillment
DB DB
/current_user
Who?

61. MonolithFulfillment
DB DB
Products

62. MonolithFulfillment
DB DB
Order
Valid?Order

63. MonolithFulfillment
DB DB
Packaging
Create

64. Rail-way oriented
programming!

65. Railway Oriented Programming

66. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end

67. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end
Validate internally

68. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end
Validate externally

69. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end
Save

70. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end
Done

71. defmodule Fulfillment.OrderCreation do
def create(params, customer, auth) do
with {:ok, order} <- validate_order(params, customer),
{:ok, order} <- validate_in_backend(order, auth),
{:ok, order} <- Repo.insert(order) do
{:ok, order}
else
{:error, changeset} -> {:error, changeset}
end
end
end
Error

72. No Kafka/Message Queue?

73. Be careful with new
technologies!

74. Microservices!

75. Microservices!
”Macroapplications”

76. All challenges are
clearly technical

77. All challenges are
clearly technical

78. Stakeholders

79. Your team

80. First Major Version

81. Get the others on board

82. Workshops

83. To know it,
you got to build it

85. Pair Adopter with Alchemist

86. Pair Adopter with Alchemist
Alchemist doesn’t touch keyboard

87. Knowledge

88. Knowledge

89. “We are still using this
like Rails – we should
use GenServers!”
Someone on your team

90. You don’t need to kill
your Monolith,
Complement it

91. Your Apps

92. Enjoy using Elixir effectively to help
your company
Tobias Pfeiffer
@PragTob
pragtob.info