If you use consumer groups to consume log data, you do not need to consider factors such as Log Service implementation, load balancing among consumers, or failovers that may occur. You can focus on business logic during log data consumption.
Prerequisites
Terms
Term | Description |
---|---|
consumer group | You can use consumer groups to consume data in Log Service. Each consumer group consists of multiple consumers. All consumers in a consumer group consume data in a Logstore. The data consumed by one consumer cannot be consumed by another consumer. You can create up to 30 consumer groups for a Logstore. |
consumer | The consumers in a consumer group consume data. The name of each consumer in a consumer group must be unique. |
Logstore | A Logstore in Log Service is a unit that is used to collect, store, and query log data. For more information, see Logstore. |
shard | A shard is used to control the read and write capacity of a Logstore. In Log Service, data is stored in shards. Each shard has an MD5 hash range, and each range is a left-closed and right-open interval. Each range does not overlap with the ranges of other shards. Each range must be within the entire MD5 hash range [00000000000000000000000000000000,ffffffffffffffffffffffffffffffff). For more information, see Shard. |
checkpoint | A checkpoint is the position at which a program stops consuming data. If the program is restarted, it consumes data from the last checkpoint. |
- Each shard can be allocated to only one consumer.
- A consumer can consume data from multiple shards.
After a new consumer is added to a consumer group, the shards allocated to the consumer group are reallocated to each consumer for load balancing. The shards are reallocated based on the preceding rules.
When you use consumer groups to consume data, Log Service stores checkpoints. Consumers can resume data consumption from a checkpoint without repeatedly consuming data after a program fault is resolved.
Procedure
You can use Log Service SDK for Java, C++, Python, or Go to create consumer groups and consume data. In this example, Log Service SDK for Java is used.
Use the Log Service console to view the status of a consumer group
- Log on to the Log Service console.
- In the Projects section, click the name of the project that you want to view.
- Click the
icon of the Logstore that you want to view and click Data Consumption.
- Click a consumer group to view the data consumption progress of each shard.
Use code to view the status of a consumer group
import java.util.List;
import com.aliyun.openservices.log.Client;
import com.aliyun.openservices.log.common.Consts.CursorMode;
import com.aliyun.openservices.log.common.ConsumerGroup;
import com.aliyun.openservices.log.common.ConsumerGroupShardCheckPoint;
import com.aliyun.openservices.log.exception.LogException;
public class ConsumerGroupTest {
static String endpoint = "";
static String project = "";
static String logstore = "";
static String accesskeyId = "";
static String accesskey = "";
public static void main(String[] args) throws LogException {
Client client = new Client(endpoint, accesskeyId, accesskey);
// Obtain all consumer groups that are created for the Logstore. If no consumer group exists, an empty string is returned.
List<ConsumerGroup> consumerGroups = client.ListConsumerGroup(project, logstore).GetConsumerGroups();
for(ConsumerGroup c: consumerGroups){
// Display the properties of consumer groups. The properties of a consumer group include the name, heartbeat timeout period, and whether the consumer group consumes data in order.
System.out.println("Name: " + c.getConsumerGroupName());
System.out.println("Heartbeat timeout period: " + c.getTimeout());
System.out.println("Ordered consumption: " + c.isInOrder());
for(ConsumerGroupShardCheckPoint cp: client.GetCheckPoint(project, logstore, c.getConsumerGroupName()).GetCheckPoints()){
System.out.println("shard: " + cp.getShard());
// The consumption time. The time is a long integer and is accurate to microseconds.
System.out.println("The time when data was last consumed: " + cp.getUpdateTime());
System.out.println("Consumer name: " + cp.getConsumer());
String consumerPrg = "";
if(cp.getCheckPoint().isEmpty())
consumerPrg = "Consumption is not started";
else{
// The UNIX timestamp. Unit: seconds. Format the output value of the timestamp.
try{
int prg = client.GetPrevCursorTime(project, logstore, cp.getShard(), cp.getCheckPoint()).GetCursorTime();
consumerPrg = "" + prg;
}
catch(LogException e){
if(e.GetErrorCode() == "InvalidCursor")
consumerPrg = "Invalid. The previous point in time when data was consumed is out of the retention period of the data in the Logstore";
else{
//internal server error
throw e;
}
}
}
System.out.println("Consumption progress: " + consumerPrg);
String endCursor = client.GetCursor(project, logstore, cp.getShard(), CursorMode.END).GetCursor();
int endPrg = 0;
try{
endPrg = client.GetPrevCursorTime(project, logstore, cp.getShard(), endCursor).GetCursorTime();
}
catch(LogException e){
//do nothing
}
// The UNIX timestamp. Unit: seconds. Format the output value of the timestamp.
System.out.println("The time when the last data record was received: " + endPrg);
}
}
}
}
Name: etl-6cac01c571d5a4b933649c04a7ba215b
Heartbeat timeout period: 60
Ordered consumption: false
shard: 0
The time when data was last consumed: 1639555453575211
Consumer name: etl-356464787983a3d17086a9797e3d5f0e6959b066-256521
Consumption progress: 1639555453
The time when the last data record was received: 1639555453
shard: 1
The time when data was last consumed: 1639555392071328
Consumer name: etl-356464787983a3d17086a9797e3d5f0e6959b066-256521
Consumption progress: 1639555391
The time when the last data record was received: 1639555391
Name: etl-2bd3fdfdd63595d56b1ac24393bf5991
Heartbeat timeout period: 60
Ordered consumption: false
shard: 0
The time when data was last consumed: 1639555453256773
Consumer name: etl-532719dd2f198b3878ee3c6dfc80aeffb39ee48b-061390
Consumption progress: 1639555453
The time when the last data record was received: 1639555453
shard: 1
The time when data was last consumed: 1639555392066234
Consumer name: etl-532719dd2f198b3878ee3c6dfc80aeffb39ee48b-061390
Consumption progress: 1639555391
The time when the last data record was received: 1639555391
Name: consumerGroupX
Heartbeat timeout period: 60
Ordered consumption: false
shard: 0
The time when data was last consumed: 1639555434142879
Consumer name: consumer_1
Consumption progress: 1635615029
The time when the last data record was received: 1639555453
shard: 1
The time when data was last consumed: 1639555437976929
Consumer name: consumer_1
Consumption progress: 1635616802
The time when the last data record was received: 1639555391
Related operations
- Configure Log4j for troubleshooting.
We recommend that you configure Log4j for the consumer program to return error messages in consumer groups. This way, you can handle exceptions at the earliest opportunity. The following code shows a configuration file of log4j.properties:
log4j.rootLogger = info,stdout log4j.appender.stdout = org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target = System.out log4j.appender.stdout.layout = org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n
After you configure Log4j, you can view the information of exceptions that occur when you run the consumer program. The following example shows an error message:[WARN ] 2018-03-14 12:01:52,747 method:com.aliyun.openservices.loghub.client.LogHubConsumer.sampleLogError(LogHubConsumer.java:159) com.aliyun.openservices.log.exception.LogException: Invalid loggroup count, (0,1000]
- Use a consumer group to consume data that is generated from a certain point in time.
// consumerStartTimeInSeconds specifies that the data generated after the point in time is consumed. public LogHubConfig(String consumerGroupName, String consumerName, String loghubEndPoint, String project, String logStore, String accessId, String accessKey, int consumerStartTimeInSeconds); // The value of the position parameter is an enumeration variable. LogHubConfig.ConsumePosition.BEGIN_CURSOR specifies that the consumption starts from the earliest data. LogHubConfig.ConsumePosition.END_CURSOR specifies that the consumption starts from the latest data. public LogHubConfig(String consumerGroupName, String consumerName, String loghubEndPoint, String project, String logStore, String accessId, String accessKey, ConsumePosition position);
Note- You can use different constructors based on your business requirements.
- If a checkpoint is stored on the server, data consumption starts from this checkpoint.
- Reset a checkpoint.
public static void updateCheckpoint() throws Exception { Client client = new Client(host, accessId, accessKey); long timestamp = Timestamp.valueOf("2017-11-15 00:00:00").getTime() / 1000; ListShardResponse response = client.ListShard(new ListShardRequest(project, logStore)); for (Shard shard : response.GetShards()) { int shardId = shard.GetShardId(); String cursor = client.GetCursor(project, logStore, shardId, timestamp).GetCursor(); client.UpdateCheckPoint(project, logStore, consumerGroup, shardId, cursor); } }
Authorize a RAM user to access consumer groups
Before you use a RAM user to access consumer groups, you must grant the required permissions to the RAM user. For more information, see Step 2: Grant permissions to the RAM user.
Action | Description | Resource |
---|---|---|
log:GetCursorOrData (GetCursor and PullLogs) | Obtains a cursor based on the point in time when log data is generated. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName} |
log:CreateConsumerGroup | Creates a consumer group in a specified Logstore. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/${consumerGroupName} |
log:ListConsumerGroup | Queries all consumer groups of a specified Logstore. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/* |
log:ConsumerGroupUpdateCheckPoint | Updates the consumption checkpoint for a shard of a specified consumer group. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/${consumerGroupName} |
log:ConsumerGroupHeartBeat | Sends a heartbeat packet for a consumer to Log Service. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/${consumerGroupName} |
log:UpdateConsumerGroup | Modifies the properties of a specified consumer group. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/${consumerGroupName} |
log:GetConsumerGroupCheckPoint | Retrieves the consumption checkpoints for one or all shards of a specified consumer group. | acs:log:${regionName}:${projectOwnerAliUid}:project/${projectName}/logstore/${logstoreName}/consumergroup/${consumerGroupName} |
{
"Version": "1",
"Statement": [
{
"Effect": "Allow",
"Action": [
"log:GetCursorOrData"
],
"Resource": "acs:log:cn-hangzhou:174649****602745:project/project-test/logstore/logstore-test"
},
{
"Effect": "Allow",
"Action": [
"log:CreateConsumerGroup",
"log:ListConsumerGroup"
],
"Resource": "acs:log:cn-hangzhou:174649****602745:project/project-test/logstore/logstore-test/consumergroup/*"
},
{
"Effect": "Allow",
"Action": [
"log:ConsumerGroupUpdateCheckPoint",
"log:ConsumerGroupHeartBeat",
"log:UpdateConsumerGroup",
"log:GetConsumerGroupCheckPoint"
],
"Resource": "acs:log:cn-hangzhou:174649****602745:project/project-test/logstore/logstore-test/consumergroup/consumergroup-test"
}
]
}