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Refactor metrics/cloudwatch #1202

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merged 2 commits into from
Nov 23, 2021
Merged

Refactor metrics/cloudwatch #1202

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4801a9b
Refactor metrics/cloudwatch:
sina-devel Nov 21, 2021
af8d701
Remove the `apply` method
sina-devel Nov 21, 2021
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30 changes: 16 additions & 14 deletions metrics/cloudwatch/cloudwatch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,11 +23,6 @@ const (
maxValuesInABatch = 150
)

type Percentiles []struct {
s string
f float64
}

// CloudWatch receives metrics observations and forwards them to CloudWatch.
// Create a CloudWatch object, use it to create metrics, and pass those metrics as
// dependencies to the components that will use them.
Expand All @@ -46,15 +41,18 @@ type CloudWatch struct {
numConcurrentRequests int
}

type option func(*CloudWatch)
// Option is a function adapter to change config of the CloudWatch struct
type Option func(*CloudWatch)

func (s *CloudWatch) apply(opt option) {
func (cw *CloudWatch) apply(opt Option) {
if opt != nil {
opt(s)
opt(cw)
}
}

func WithLogger(logger log.Logger) option {
// WithLogger sets the Logger that will receive error messages generated
// during the WriteLoop. By default, fmt logger is used.
func WithLogger(logger log.Logger) Option {
return func(c *CloudWatch) {
c.logger = logger
}
Expand All @@ -64,7 +62,7 @@ func WithLogger(logger log.Logger) option {
// existing/default values.
// Reason is that Cloudwatch makes you pay per metric, so you can save half the money
// by only using 2 metrics instead of the default 4.
func WithPercentiles(percentiles ...float64) option {
func WithPercentiles(percentiles ...float64) Option {
return func(c *CloudWatch) {
c.percentiles = make([]float64, 0, len(percentiles))
for _, p := range percentiles {
Expand All @@ -76,7 +74,11 @@ func WithPercentiles(percentiles ...float64) option {
}
}

func WithConcurrentRequests(n int) option {
// WithConcurrentRequests sets the upper limit on how many
// cloudwatch.PutMetricDataRequest may be under way at any
// given time. If n is greater than 20, 20 is used. By default,
// the max is set at 10 concurrent requests.
func WithConcurrentRequests(n int) Option {
return func(c *CloudWatch) {
if n > maxConcurrentRequests {
n = maxConcurrentRequests
Expand All @@ -89,7 +91,7 @@ func WithConcurrentRequests(n int) option {
// Namespace is applied to all created metrics and maps to the CloudWatch namespace.
// Callers must ensure that regular calls to Send are performed, either
// manually or with one of the helper methods.
func New(namespace string, svc cloudwatchiface.CloudWatchAPI, options ...option) *CloudWatch {
func New(namespace string, svc cloudwatchiface.CloudWatchAPI, options ...Option) *CloudWatch {
cw := &CloudWatch{
sem: nil, // set below
namespace: namespace,
Expand All @@ -102,8 +104,8 @@ func New(namespace string, svc cloudwatchiface.CloudWatchAPI, options ...option)
percentiles: []float64{0.50, 0.90, 0.95, 0.99},
}

for _, optFunc := range options {
optFunc(cw)
for _, opt := range options {
cw.apply(opt)
}
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Can we just remove the apply method altogether?

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It's actually more safer than a simple function. apply cannot be called outside of the package, but with the current Option type it's possible to modify the state of Cloudwatch after the initialization.

I'd instead change the signature of Option to this:

type Option interface{
    apply(*CloudWatch)
}

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@peterbourgon peterbourgon Nov 21, 2021 •
edited
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I'd instead change the signature of Option to this:

Strong -1. Option interfaces are an antipattern, and especially those that take this form, i.e. an exported interface with an unexported method. type Option func(*Cloudwatch) keeps the Options grouped with the type in the docs, which is important.

with the current Option type it's possible to modify the state of Cloudwatch after the initialization.

I understand your point, but I don't think this is a meaningful risk, as only Options defined in package cloudwatch have access to the unexported fields of the struct.

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I think we can remove the apply method, because cloudwatch.New(namespace, svc, nil) isn't norm.

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fixed


cw.sem = make(chan struct{}, cw.numConcurrentRequests)
Expand Down