mirror of
https://github.com/rocky-linux/peridot.git
synced 2024-12-30 05:50:56 +00:00
146 lines
5.7 KiB
Markdown
146 lines
5.7 KiB
Markdown
# DynamoDB Lock Client for Go
|
|
|
|
[](https://godoc.org/cirello.io/dynamolock)
|
|
[](https://travis-ci.org/cirello-io/dynamolock)
|
|
[](https://coveralls.io/github/cirello-io/dynamolock?branch=master)
|
|
[](https://goreportcard.com/report/github.com/cirello-io/dynamolock)
|
|
[](https://github.com/cirello-io/public/blob/master/SLA.md)
|
|
|
|
This repository is covered by this [SLA](https://github.com/cirello-io/public/blob/master/SLA.md).
|
|
|
|
The dymanoDB Lock Client for Go is a general purpose distributed locking library
|
|
built for DynamoDB. The dynamoDB Lock Client for Go supports both fine-grained
|
|
and coarse-grained locking as the lock keys can be any arbitrary string, up to a
|
|
certain length. Please create issues in the GitHub repository with questions,
|
|
pull request are very much welcome.
|
|
|
|
It is a port in Go of Amazon's original [dynamodb-lock-client](https://github.com/awslabs/dynamodb-lock-client).
|
|
|
|
## Use cases
|
|
A common use case for this lock client is:
|
|
let's say you have a distributed system that needs to periodically do work on a
|
|
given campaign (or a given customer, or any other object) and you want to make
|
|
sure that two boxes don't work on the same campaign/customer at the same time.
|
|
An easy way to fix this is to write a system that takes a lock on a customer,
|
|
but fine-grained locking is a tough problem. This library attempts to simplify
|
|
this locking problem on top of DynamoDB.
|
|
|
|
Another use case is leader election. If you only want one host to be the leader,
|
|
then this lock client is a great way to pick one. When the leader fails, it will
|
|
fail over to another host within a customizable leaseDuration that you set.
|
|
|
|
## Getting Started
|
|
To use the DynamoDB Lock Client for Go, you must make it sure it is present in
|
|
`$GOPATH` or in your vendor directory.
|
|
|
|
```sh
|
|
$ go get -u cirello.io/dynamolock
|
|
```
|
|
|
|
This package has the `go.mod` file to be used with Go's module system. If you
|
|
need to work on this package, use `go mod edit -replace=cirello.io/dynamolock@yourlocalcopy`.
|
|
|
|
Then, you need to set up a DynamoDB table that has a hash key on a key with the
|
|
name `key`. For your convenience, there is a function in the package called
|
|
`CreateTable` that you can use to set up your table, but it is also possible to
|
|
set up the table in the AWS Console. The table should be created in advance,
|
|
since it takes a couple minutes for DynamoDB to provision your table for you.
|
|
The package level documentation comment has an example of how to use this
|
|
package. Here is some example code to get you started:
|
|
|
|
```Go
|
|
package main
|
|
|
|
import (
|
|
"log"
|
|
|
|
"cirello.io/dynamolock"
|
|
"github.com/aws/aws-sdk-go/aws"
|
|
"github.com/aws/aws-sdk-go/aws/session"
|
|
"github.com/aws/aws-sdk-go/service/dynamodb"
|
|
)
|
|
|
|
func main() {
|
|
svc := dynamodb.New(session.Must(session.NewSession(&aws.Config{
|
|
Region: aws.String("us-west-2"),
|
|
})))
|
|
c, err := dynamolock.New(svc,
|
|
"locks",
|
|
dynamolock.WithLeaseDuration(3*time.Second),
|
|
dynamolock.WithHeartbeatPeriod(1*time.Second),
|
|
)
|
|
if err != nil {
|
|
log.Fatal(err)
|
|
}
|
|
defer c.Close()
|
|
|
|
log.Println("ensuring table exists")
|
|
c.CreateTable("locks",
|
|
dynamolock.WithProvisionedThroughput(&dynamodb.ProvisionedThroughput{
|
|
ReadCapacityUnits: aws.Int64(5),
|
|
WriteCapacityUnits: aws.Int64(5),
|
|
}),
|
|
dynamolock.WithCustomPartitionKeyName("key"),
|
|
)
|
|
|
|
data := []byte("some content a")
|
|
lockedItem, err := c.AcquireLock("spock",
|
|
dynamolock.WithData(data),
|
|
dynamolock.ReplaceData(),
|
|
)
|
|
if err != nil {
|
|
log.Fatal(err)
|
|
}
|
|
|
|
log.Println("lock content:", string(lockedItem.Data()))
|
|
if got := string(lockedItem.Data()); string(data) != got {
|
|
log.Println("losing information inside lock storage, wanted:", string(data), " got:", got)
|
|
}
|
|
|
|
log.Println("cleaning lock")
|
|
success, err := c.ReleaseLock(lockedItem)
|
|
if !success {
|
|
log.Fatal("lost lock before release")
|
|
}
|
|
if err != nil {
|
|
log.Fatal("error releasing lock:", err)
|
|
}
|
|
log.Println("done")
|
|
}
|
|
```
|
|
|
|
## Selected Features
|
|
### Send Automatic Heartbeats
|
|
When you create the lock client, you can specify `WithHeartbeatPeriod(time.Duration)`
|
|
like in the above example, and it will spawn a background goroutine that
|
|
continually updates the record version number on your locks to prevent them from
|
|
expiring (it does this by calling the `SendHeartbeat()` method in the lock
|
|
client.) This will ensure that as long as your application is running, your
|
|
locks will not expire until you call `ReleaseLock()` or `lockItem.Close()`
|
|
|
|
### Read the data in a lock without acquiring it
|
|
You can read the data in the lock without acquiring it, and find out who owns
|
|
the lock. Here's how:
|
|
```Go
|
|
lock, err := lockClient.Get("kirk");
|
|
```
|
|
|
|
## Logic to avoid problems with clock skew
|
|
The lock client never stores absolute times in DynamoDB -- only the relative
|
|
"lease duration" time is stored in DynamoDB. The way locks are expired is that a
|
|
call to acquireLock reads in the current lock, checks the RecordVersionNumber of
|
|
the lock (which is a GUID) and starts a timer. If the lock still has the same
|
|
GUID after the lease duration time has passed, the client will determine that
|
|
the lock is stale and expire it.
|
|
|
|
What this means is that, even if two different machines disagree about what time
|
|
it is, they will still avoid clobbering each other's locks.
|
|
|
|
## Required DynamoDB Actions
|
|
For an IAM role to take full advantage of `dynamolock`, it must be allowed to
|
|
perform all of the following actions on the DynamoDB table containing the locks:
|
|
|
|
* `GetItem`
|
|
* `PutItem`
|
|
* `UpdateItem`
|
|
* `DeleteItem`
|