In this presentation, we're discussing whether we need API gateway or not on Micro-Services Architecture. We'll see pros and cons of several ways how clients access to services. [Updated : 13 Jan 2015] Additional cons of API gateway is added, as commented by Hyunsik Kang(강현식), Coupang.

1. API Gateway : To be or not to be?
Platform Architecture Team
SK Planet

2. Synopsis
• You’re developing based on MSA(Micro-
Services Architecture)
• How do the clients access the individual
Micro-services?

3. #1 : I don’t care for clients, DIY
Client A
(Web)
Client B
(App)
MS-A
MS-ALB
MS-A
MS-BLB
MS-A
MS-CLB
MS-A
MS-DLB
Security
Logging
Version
…
Security
Logging
Version
…
Security
Logging
Version
…
Security
Logging
Version
…

4. #1 : I don’t care for clients, DIY
• Clients need to access individual Micro-Services by themselves
• Pros
– No SPOF
– No cost for developing API Gateway
• Cons
– Clients need to know endpoints of Micro-Services
– If Micro-Services changes something(ex: LB VIP), all clients need to update
– Each Micro-Services needs to handle these by themselves
• Securities to protect their APIs (Auth, ACL, IP Blacklist, Rate Limiting, …), Versioning
• Logging, Analytics, and any requirements from clients (ex : Batch APIs)
– You’re adding another security path whenever new Micro-Service is added
– If there is no API standard nor API spec sharing point between Micro-Services,
clients will go to hell
– Cannot handle composition scenario to prevent REST chattiness problem
– You need to place Load Balancer in front of each Micro-services and consider
fail-over of LB, too

5. #2 : Wrapper (Library/SDK)
Wrapper
*
Wrapper
*
MS-A
MS-ALB
MS-A
MS-BLB
MS-A
MS-CLB
MS-A
MS-DLB
Client A
(Web)
Client B
(App)
* Wrapper could be created
by individual Micro-Services
Security
Logging
Version
…
Security
Logging
Version
…
Security
Logging
Version
…
Security
Logging
Version
…

6. #2 : Wrapper (Library/SDK)
• Clients use Wrapper(Library/SDK) to access Micro-Services
• Pros
– No SPOF
– No cost for developing API Gateway
– Higher Abstraction than REST APIs, so easy to use
• Cons
– Clients Wrapper needs to know endpoints of Micro-Services
– If Micro-Services changes something(ex: LB VIP), all clients need to update
Wrapper needs to be updated, QA, and re-deployed
– Wrapper is responsible for backward compatibility
– Each Micro-Services needs to handle these by themselves
• Securities to protect their APIs (Auth, ACL, IP Blacklist, Rate Limiting, …), Versioning, Logging, Analytics,
and any requirements from clients (ex : Batch APIs)
– You’re adding another security path whenever new Micro-Service is added
– If there is no API standard nor API spec sharing point between Micro-Services, clients will go
to hell
You need to update Wrapper document/manual, provide download location, manage achieve,
maintain release notes, send notices, and maybe cause forced-update of your app
– Cannot handle composition scenario to prevent REST chattiness problem,
but need to update/re-deploy your wrapper
– You need to place Load Balancer in front of each Micro-services and consider fail-over of LB,
too
– Becoming big burden if you need to support polyglot clients

7. Checkpoint
• It’s all about level of “Abstraction”
– Provide it as REST APIs
– Provide it as Wrapper (Library/Wrapper)
• Higher abstraction
– Makes client happy (but only if you maintain versions/backward
compatibility well)
– Makes Wrapper developer unhappy
– Even worst if API Provider != Wrapper developer
• Common RoR problems
– If client fails, who’s responsible for investigate it?
While stacktraces says problem is raised on the Wrapper, they
will call Wrapper developer even though client mis-use wrapper
or server fails 

8. API Gateway
#3 : API Gateway
Client A
(Web)
Client B
(App)
MS-A
MS-A
MS-A
MS-B
MS-A
MS-C
MS-A
MS-D
Security
Logging
Version
…

9. #3 : API Gateway
• Single endpoint for clients, handle requests proxied/routed to the
appropriate service (or service instance)
• Pros
– Can solve most problems
– Separation of Concerns
• Micro-Services focus on business features
• API Gateway provides protection/common feature layer
– Minimize/Isolate services’ change impacts
• Cons
– Possibility of SPOF/bottleneck
– Performance tradeoff due to processing time in API Gateway and more
network hops
– Need to manage routing rule or APIs
– Needs Service Discovery/Registry
– Cost for developing API Gateway
– Additional Hardware/Network/Management cost
– Risk of management bottleneck

10. SPOF/bottleneck : Scale-out
API Gateway
Client A
(Web)
Client B
(App)
MS-A
MS-A
MS-A
MS-B
MS-A
MS-C
MS-A
MS-D
Security
Logging
Version
… API Gateway
Security
Logging
Version
…
LB

11. SPOF/bottleneck : Partitioning
API Gateway
Client A
(Web)
Client B
(App)
MS-A
MS-A
MS-A
MS-B
MS-A
MS-C
MS-A
MS-D
Security
Logging
Version
…
API Gateway
Security
Logging
Version
…
LB
API Gateway
Security
Logging
Version
…
API Gateway
Security
Logging
Version
…
LB
DNS/
LB
A or B
C or D

12. SPOF/bottleneck : Partitioning
API GatewayClient A
(Web)
Client B
(App)
MS-A
MS-A
MS-A
MS-B
MS-A
MS-C
MS-A
MS-D
Security
Logging
Version
…
API Gateway
Security
Logging
Version
…
LB
API Gateway
Security
Logging
Version
…
API Gateway
Security
Logging
Version
…
LB

13. Performance Tradeoff
• Network hop/latency depends on network
topology
• API Gateway processing time depends on
what you want to do in API Gateway
• Consider Tradeoff : What’s more important?
• Some Tips
– Don’t parse request/response body if you don’t
need it
– Caching on API Gateway

14. Managing Routing Rule or APIs
• Routing Rule-based Control
– Define Coarse-grained routing rule
– Gateway knows MSs but don’t care for specific APIs
– Micro-Services need to resolve APIs and validate
whether they are valid request
• API-based Control
– Register APIs want to be managed in Gateway
– API Gateway resolve APIs and validate
request/response with exact match
– Gateway should know APIs

15. Managing Routing Rule or APIs
Client A
(Web)
API Gateway MS-A
/A/InvalidResources
with ValidCredential
/InvalidResources
404 Not Found404 Not Found
Security : Passed
Client A
(Web) API Gateway
/A/InvalidResources
with ValidCredential
404 Not Found
Security : Passed
/A/* -> MS-A
/A/ValidResources -> MS-A/ValidResources
- params : …
- result: …
MS-A
/A/ValidResources?invalid
with ValidCredential
400 Bad Request
(Invalid Parameter)
/A/ValidResources?invalid
with ValidCredential
400 Bad Request
(Invalid Parameter)
/A/ValidResources?invalid
with ValidCredential
400 Bad Request
(Invalid Parameter)
Routing Rule Based Control(per MS)
API Based Control (per API)

16. Managing Routing Rules or APIs
• Routing rule based is preferred when
• Clients are 1st parties
• Coarse-grained control is enough
• You can provide API spec/document from Micro-Services directly
• API is changed frequently
• API based is preferred when
• Clients are including 3rd parties
• Minimize Micro-Services’ overhead from invalid request
• Fine-grained control is needed
• If you require mediation or some manipulation per APIs
• You need to provide API spec/document from API Gateway
• Recommendations
– Use routing rule based control primarily, then append API-based
control as you need

17. Managing API specification
• You can manage it
– Deeply coupled with API Gateway
API-based Control requires for API Gateway to
know API specification
– Externally (ex : Swagger, ProtocolBuffer)
Both Routing Rule-based and API-based control
• If you have a API spec,
– Client developer can create client codes (even
wrapper)
– Server developer can create server codes

18. Service Discovery/Registry
MS-A Container
API
Gateway
UI
UI
MS-A
HA Proxy
HA Proxy
HA Proxy
Service
Registry
Service Agent
MS-A Container
MS-A HA Proxy
Service Agent
MS-B Container
MS-B
Service Agent
MS-B Container
MS-B
Service Agent

19. Cost for developing API Gateway
• Depends on what you want to do with API
Gateway
• Simple requirements = Simple API Gateway
(nginx/HA proxy might be enough for you)
• Node.js is a good start point to implement
• But going complex
– If you need to consider 3rd parties and Open API since
Developer portal and Onboarding process is required
– If you want some GUI and management console (=
Publisher portal)
– Consider API Gateway as Silver Bullet (ESB?)…

20. Additional
Hardware/Network/Management cost
• Another tradeoff : What’s more important?
• Depends on how you implement it and what
you want to do
• Cost could be issue
– If you consider adopting commercial products
– If you consider doing a lot of manipulation in API
Gateway

21. Risk of management bottleneck
• If API Gateway is managed by single team,
there are risks of management bottleneck
– API Gateway team has primary responsibility for
changes/failure/backward compatibility, …
– API Gateway team could be a bottleneck (going
worse if you do a lot of manipulations in it)
• Recommendation : separate managements
– API Gateway itself (API Gateway team)
– Services on the API Gateway (each service teams)

22. API Gateway: To be or not to be
• Consider your scenario
• But generally,
API Gateway is a good choice…
and it begins API Managements of your
organization
• To adopt it, start with simple one
– again, nginx/HA proxy might be enough for you
– Consider complex product/solution later

23. Send a feedback
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