AWS Lambda has changed the way we deploy and run software, but the serverless paradigm has created new challenges to old problems: How do you test a cloud-hosted function locally? How do you monitor them? What about logging and config management? And how do we start migrating from existing architectures?
Yan Cui shares solutions to these challenges, drawing on his experience running Lambda in production and migrating from an existing monolithic architecture.
8. hidden complexities and dependencies
low utilisation to leave room for traffic spikes
EC2 scaling is slow, so scale earlier
lots of cost for unused resources
up to 30 mins for deployment
deployment required downtime
9. - Dan North
“lead time to someone saying
thank you is the only reputation
metric that matters.”
65. “…We find that tests that mock external
libraries often need to be complex to
get the code into the right state for the
functionality we need to exercise.
The mess in such tests is telling us that
the design isn’t right but, instead of
fixing the problem by improving the
code, we have to carry the extra
complexity in both code and test…”
Don’t Mock Types You Can’t Change
66. “…The second risk is that we have to be
sure that the behaviour we stub or mock
matches what the external library will
actually do…
Even if we get it right once, we have to
make sure that the tests remain valid
when we upgrade the libraries…”
Don’t Mock Types You Can’t Change
72. is our request correct?
is the request mapping
set up correctly?is the API resources
configured correctly?
are we assuming the
correct schema?
LambdaAPI Gateway DynamoDB
is Lambda proxy
configured correctly?
is IAM policy set
up correctly?
is the table created?
what unit tests will not tell you…
73.
74. most Lambda functions are simple
have single purpose, the risk of
shipping broken software has largely
shifted to how they integrate with
external services
observation
75.
76. But it slows down
my feedback loop…
IT’S NOT
ABOUT YOU!
77. …if a service can’t provide
you with a relatively easy
way to test the interface in
reality, then you should
consider using another one.
Paul Johnston
78. “…Wherever possible, an acceptance
test should exercise the system end-to-
end without directly calling its internal
code.
An end-to-end test interacts with the
system only from the outside: through
its interface…”
Testing End-to-End
89. “the earlier you consider CI + CD, the
more time you save in the long run”
- me
90. “…We prefer to have the end-to-end
tests exercise both the system and the
process by which it’s built and
deployed…
This sounds like a lot of effort (it is), but
has to be done anyway repeatedly
during the software’s lifetime…”
Testing End-to-End
138. console.log(“hydrating yubls from db…”);
console.log(“fetching user info from user-api”);
console.log(“MONITORING|1489795335|27.4|latency|user-api-latency”);
console.log(“MONITORING|1489795335|8|count|yubls-served”);
timestamp metric value
metric type
metric namemetrics
logs
187. complexity ceiling of a
Node.js app
complexity
referential transparency
immutability as default
type inference
option types
union types
…
188. for managing complexity
complexity ceiling of a
Node.js app
complexity
referential transparency
immutability as default
type inference
option types
union types
…
189. complexity ceiling of a
Node.js app
complexity
complexity ceiling of a
Node.js Lambda function
190. if you can limit the complexity
of your solution, maybe you
won’t need the tools for
managing that complexity.
me
201. “AWS Lambda polls your stream and
invokes your Lambda function. Therefore, if
a Lambda function fails, AWS Lambda
attempts to process the erring batch of
records until the time the data expires…”
http://docs.aws.amazon.com/lambda/latest/dg/retries-on-errors.html
207. “Each shard can support up to
5 transactions per second for
reads, up to a maximum total data
read rate of 2 MB per second.”
http://docs.aws.amazon.com/streams/latest/dev/service-sizes-and-limits.html
208. “If your stream has 100 active shards,
there will be 100 Lambda functions
running concurrently. Then, each
Lambda function processes events
on a shard in the order that they arrive.”
http://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html