Default Jackson serde in Spring


We’re using Spring in most of our Java applications, and rely on Swagger for a lot of API calls. Now, having all the jackson annotations makes everything easy – until it becomes annoying, like this:

    @JsonFormat(pattern = ModelConst.JSON_DATE_FORMAT)
    private LocalDate startDate;
    @JsonFormat(pattern = ModelConst.JSON_DATE_FORMAT)
    private LocalDate endDate;
    @JsonFormat(pattern = ModelConst.JSON_DATE_FORMAT)
    private LocalDate paymentDate; 
    @JsonFormat(pattern = ModelConst.JSON_DATE_FORMAT)
    private LocalDate registrationDate; 

Now, having one of these is nice and tidy. Having them all over the model code is annoying, to say the least.

So, what do you do?

Well, with Jackson you can add custom serializers to the ObjectMapper object. Problem is, we’re using spring, so we don’t really have access to the ObjectMapper object used to do the serialization/deserialization.

The first option was to generate a bean to generate the ObjectMapper , and assign the serializers to it. However, there’s a better way – We can use a configuration bean supplied by Spring:

public class AppConfig {
    private static final String dateFormat = "yyyy-MM-dd";
    private static final String dateTimeFormat = "yyyy-MM-dd HH:mm:ss";
    public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
        return builder -> {
            builder.serializers(new LocalDateTimeSerializer(
            builder.serializers(new LocalDateSerializer(


This way, we don’t need any of the annotations, since we’ve set the default parsing.

    private LocalDate startDate;
    private LocalDate endDate;
    private LocalDate paymentDate; 
    private LocalDate registrationDate; 

Some kafka retention lessons (we learned the hard way)

We’re using Kafka (2.0 on cluster, Java client 1.1) as our messaging backbone. A different cluster is deployed in each environment, and we recently started seeing some weird behaviour in one of our user acceptance environments.

First Problem: Old messages are suddenly reprocessed.

Once in every few version releases, we suddently saw some services re-processing old messages. After a lot of head banging and tedious head scratching, we found out that in Kafka, the retention on the offsets and the retention on the messages is not necessarily the same.

What does it mean? Well, when a messsage is sent to a specific Kafka topic, it’s retained as long as the topic retention. So, if our topic retention is 1 week, then after 1 week it will no longer be available.

The consumer offset, however, is a different story. The consumers offsets are saved in an internal topic called __consumer_offsets, and their retention time is defined in the parameter offsets.retention.minutes in the broker config with a deafult of 24 hours.

So what happened to us is this: Our messages retention was set to 2 weeks, and the offsets retention was 24 hours. After a period of not using the system, we deployed a new version. Once the new version was up, it queried the Kafka topic for it’s latest offset. However, the consumer_offset of this application id was already deleted, and the default behaviour is to read from the begining of the stream – which is exactly what happened to us: This is why we were consuming old messages when we released new versions, and it would only happen if we released versions after more than 24 hours and less than 2 weeks.

Second Problem: The producer attempted to use a producer id which is not currently assigned to its transactional id

This one was even more annoying. We’re using Kafka streams api, which promises an exactly-once message processing. Every once in a while, we’d get the above error after the message has been proccessed. This would cause the Kafka stream to shut down, the app to restart – and then, to process the same message again(!).

Now, this was extremly weird. First of all, it was a violation of our "exactly-once" constraint. In addition, we had no idea what it means!

Lately we started also seeing what seems to be a related error: org.apache.kafka.common.errors.UnknownProducerIdException: Found no record of producerId=16003 on the broker. It is possible that the last message with the producerId=16003 has been removed due to hitting the retention limit.

So we started thinking – what is happening to our producer ids?

Then we discovered this:

The maximum amount of time in ms that the transaction coordinator will wait before proactively expire a producer’s transactional ID without receiving any transaction status updates from it.

Type: int

Default: 604800000

604800000 ms is 7 days. So basically, if we’ve had a streaming application that had no traffic for 7 days, it’s producer metadata was deleted – and that’s the behaviour we’ve been seeing: the application consumed the message, processed it – and when it tried to commit the transaction and update the offset, it failed. This is why we processed, crushed, and re-processed.

Bottom line

Kafka is a tool built for massive data streaming, and it’s defaults are organized around it. Both these issued occured because this specific environment’s usage pattern is random and is not corresponding with the cdefault configuration.

Lambda: Move S3 file based on content

We have a process that saves a file to an S3 bucket. We needed a lambda to read the file, parse part of the content, and move the file to the appropriate folder in the bucket – So we set up a lambda to run whenever a file is created in the base folder of the bucket, read the file, and move it to the appropriate place.

AWS Certified Solutions Architect – Associate

I’ve been doing a Udemy course as a preparation for the AWS Certified Solutions Architect – Associate. These are my summary notes

AWS Certified Solutions Architect – Associate


  • 130 minutes
  • 60 questions
  • Results are between 100 – 1000, pass: 720
  • Scenario based qestions


  • Users
  • Groups
  • Roles
  • Policis

Users are part of Groups Resources have Roles : i.e, for an instance to connect to S3, it needs to have a role All the User groups and Roles get their permissions are through Policies, which are defined by json:

# God mode policy
    "Statement": [
            "Effect": "Allow",
            "Action": "*",
            "Resource": "*"

(Creating policies is not part of the exam)


  • IAM is cross-regional
  • "root account" is the account created with the first setup of the AWS account, and has complete Admin access.
  • New users have no permissions until assigned
  • New users are assinged Access Key Id and Secret Access Keys when created, for the api access.


  • Key – Value Object based, with metadata and versioning
  • Has access control lists
  • Max 5TB file size
  • Buckets are universal namespace (https://s3-{region}{bucket})

Consistency model:

  • Read After Write consistency – object will be availabe for readdirectly after being written
  • Eventual consistency for overwrite PUTS and DELETES

Storage Tiers/Classes

  • S3 Standatrd – 99.99% availability, 99.999999999% durability, cross-devices, cross-facilities redundancy, designed to sustain loss of 2 facilities at the same time.
  • S3 – IA (infrequently access) – for data accessed less frequently. Lower storage fee, but has a retrieval fee. S3 One Zone – IA : the same as IA, only in 1 AZ. (cheaper)
  • Glacier: Very cheap, archival only. Standard retrieval time takes 3 – 5 hours.

Cross Region Replication (CRR)

  • Requires versioning enaled on the source bucket


  • Edge Location – the location the content will be cached: Per AWS Region (They are not read only, you can write to them too, and they will replicate to the origin and from there to others)
  • Clearing cache cost money 🙂
  • Origin – The original file location: S3 bucket, EC2 instance, ELB, or Route53
  • Distribution – all the locations of the Edges you defined
  • Can distribute dynamic, static, streaming and interactive content (Web Distribution: most common, for websites; RTMP – media streaming)


Placment groups

Two types:

  1. Cluster placment group – A group of instances within a single AZ that need low latency / high throughput (i.e cassandra cluster). Only available for specific types.
  2. Spread placment group – A group of instances that need to be place seperatly from each other
  • Placment group name myst be unique within aws account
  • Only available for certain instance types
  • Recommended to use homogenous instances within placment group
  • You can’t merge placment groups
  • You can’t move an exisitng instance to a placment group, only create it into it


  • Supports NFSv4
  • Only pay for used storage
  • Scales up to petabytes
  • Support thousands of concurrent NFS connections
  • Data is stored across multiple AZ within region

Route 53

DNS overview

  • NS – Name Server record. Meaning, if I go to, and I’m the first one to try it in my ISP, then the ISP server will ask the .com if it has NS recored for helloRoute53gurus. The .com will have a record that maps it to So it’ll go to , which will direct it to Route53..\
  • A – short for Address – that’s the most basic record, and it’s the IP for the url
  • TTL – time to live – how long to keep in cache
  • CNAME – resolve one domain to another (can’t be used for ‘naked’ domain names, e.g: ‘’ )
  • Alias – unique to Route53, the may resource records to Elastic Load Balancer, CloudFron, or S3 bucket that are configured as websites. They work like CNAME ( ->
  • MX record – email records
  • PTR Records – reverse lookups

ELB do not have predefined IPv4 addresses, you resolve them using a dns name. So basically, if you have the domain "" and you want to direct it’s traffic to an ELB, you need to use an Alias (not a cname, because it’s a naked domain name!, and not an A record because it has no IP)

Routing Policies

  • Simple Routing – 1 record with multiple ips addresses, randomly returned. No health checks
  • Weighted Routing – 1 record with N% goes to one rcecord, and M% to another and so forth
  • Latency Based Routing – Route 53 will send to the region with the lowest latency
  • Failover Routing – Health check based Primary/Secondary routing: if the primary instance fails (health check = false), directs to the secondary
  • Geolocation Routing – config which geo location goes to which instance
  • Multivalue Answer Routing – Several records, each with ip addresses, and health check for each resource. The ips will return randomlly, so it’s good for disparsing traffic to different resources.


  • NAT Gateways – scaled up to 10G, no need to patch/add security groups/assign ip (automatic), they do need to be updates in the routing table (so they can go out via igw)
  • Network ACL –
    • It’s like a SG, in the subnet level.
    • Each subnet is associated with one, but default it’s blocking all in/out bound traffic. you can associate multiple subnets to the same ACL, but only 1 ACL per subnet.
    • The traffic rules are evaluated from the lowest value and up.
    • Unlike SG, opening port 80 for incoming will not allow outbound response on port 80. If you want to communicate on port 80, you’d have to define rule both for inbound and outbound. (Otherwise, it’ll go in and not out)
    • You can block IP addresses using ACL, you can’t with SG
  • ALB – you need at least 2 public subnets for an Application Load Balancer

Application Services


  • Distributed Pull based Messaging queue
  • Up to 256 Kb messages
  • Default retention: 4 days, max 14 days
  • Default promisese "at-least-once", "FIFO" promises exactly once with ordering
  • Can poll with timeout (like kafka)
  • Visibility – once message is consumed, it’s marked as "invisible" for 30 seconds (default, max is 12 hours), and if it’s not marked as "read" within that time frame, it returns to be visible and re-distributed to another consumer.

SWF – Simple Workflow Service

  • Kind on amazon ETL system, with Workers (who process jobs) and Deciders (who control the flow of jobs). The system enables dispatching of jobs to multiple workers (which makes it easily scalable), tracking the jobs status, and so forth.
  • SWF keeps track of all the tasks and events in an application (in SQS you’d have to do it manually)
  • Unlike SQS, In SWF a task is assigned only once and never duplicated (What happens if the job fails? IDK).
  • SWF enables you to incorportae human interaction – like, if someone needs to approve received messages, for example

SNS – Simple Notifications Services

Delivers notification too:

  • Push notifications

  • SMS

  • Email

  • SQS queue

  • Any http endpoint

  • Lamda functions

  • Messages are hosted in multiple AZ for redundancy

Messages are agregated by Topics, and recipients can dynamically subscribe to Topics.

Elastic Transcoder

  • Convert video files between formats – like formatiing video files to different formats for portable devices

API Gateway

Basically a front API for your lamda/internal APIs, with amazon capabilities:

  • API Caching – caching responses to an request api with TTL
  • Throttling requests to prevent attacks


3 types:

  • Streams – Kafka (Retention : up to 7 days) – Shards = partitions (?)
  • Firehose – Fully automated, no consumers, No retention, No shards – Can be written to s3 / elastic
  • Analytics – run SQL queries on the streams/firehose streams, and write the result to s3 /elsastic

Basic Lambda to call internal VPC api

Product team decided they wanted a specific event to happen every time a specific email address receives an email. The first option was to poll mail server and analyse all the received emails (yuck!).

The other option was to use AWS tools. In our case, forward the email to SES and call a lambda that will trigger our internal service with all the email meta-data – Which is exactly what we did.

Few pointers before the code:

  1. Lambda doesn’t load node dpendencies – so if you want to use some external packages except aws, you’d need to upload a zip with the dependencies and your code
  2. If you want to call an internal VPC resource, you need to:
    1. Assign the lambda to your VPC
    2. Assign the lambda a security group that will enable it to work from within the vpc

After you’ve assigned the Lambda to the VPC and setup the SG, the rest is easy:

const axios = require('axios'); //Loaded in the zip file!

console.log(`Url: http://${process.env.SERVICE_URL}`)

exports.handler = (event, context, callback) => {
    console.log(`Inside lambda: ${JSON.stringify(event)}` )`http://${process.env.SERVICE_URL}`, event)
        .then((res) => {
            callback(null, res);
        .catch((error) => {
    console.log(`Logging out`)    

You can find all the event types here: Sample Events

The SES -> Lambda invocation only send the Email’s meta-data. If you want to have the email content, you’d need to use SNS (so SES -> SNS Topic -> Lambda), but bear in mind that SNS only supports emails up to 150K, so for anything larger, you’d need to move to S3

Postgres – Logging queries

We had an issue with some JQL queries returning weird results from the db, so we wanted to see exactly what’s arriving to the psql service. To see that:

  1. Edit the config file: /var/lib/postgresql/data/postgresql.conf

  2. Unmark and change the following:

#logging_collector = off                # Enable capturing of stderr and csvlog
                                        # into log files. Required to be on for
                                        # csvlogs.
                                        # (change requires restart)

# These are only used if logging_collector is on:
#log_directory = 'pg_log'               # directory where log files are written,
                                        # can be absolute or relative to PGDATA
#log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'        # log file name pattern,
                                        # can include strftime() escapes
log_statement = 'none'                   # none, ddl, mod, all
  • The logging_collector should be set to on to enable logging
  • The log_statement should be set to all to enable query logging
  • The log_directory and log_filename can stay the same, depends on what you want.

So your line should look like:

#logging_collector = on                # Enable capturing of stderr and csvlog
                                        # into log files. Required to be on for
                                        # csvlogs.
                                        # (change requires restart)

# These are only used if logging_collector is on:
#log_directory = 'pg_log'               # directory where log files are written,
                                        # can be absolute or relative to PGDATA
#log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'        # log file name pattern,
                                        # can include strftime() escapes
log_statement = 'all'                   # none, ddl, mod, all

Now restart your service, and you’re good to go : the logs will be at /var/lib/postgresql/data/pg_log

Don’t run this on production, as it will seriously fuck up your performance!

AWS Re:Invent 2018 – My Top Sessions

I’m planning to upload a different post on each one of the sessions I liked at the Re:Invent 2018, but for now, just to have everything at one place, here is the short list:

SVR322 – From Monolith to Modern Apps: Best Practices

We are a lean team consisting of developers, lead architects, business analysts, and a project manager. To scale our applications and optimize costs, we need to reduce the amount of undifferentiated heavy lifting (e.g., patching, server management) from our projects. We have identified AWS serverless services that we will use. However, we need approval from a security and cost perspective. We need to build a business case to justify this paradigm shift for our entire technology organization. In this session, we learn to migrate existing applications and build a strategy and financial model to lay the foundation to build everything in a truly serverless way on AWS.


ARC337 – Closing Loops and Opening Minds: How to Take Control of Systems, Big and Small

Whether it’s distributing configurations and customer settings, launching instances, or responding to surges in load, having a great control plane is key to the success of any system or service. Come hear about the techniques we use to build stable and scalable control planes at Amazon. We dive deep into the designs that power the most reliable systems at AWS. We share hard-earned operational lessons and explain academic control theory in easy-to-apply patterns and principles that are immediately useful in your own designs.


ARC403 – Resiliency Testing: Verify That Your System Is as Reliable as You Think”

In this workshop, we illustrate how to set up your own resiliency testing. We set up a simple three-tier architecture and explore the failure modes with Bash and Python scripts. To participate, you need an account that can run AWS CloudFormation, AWS Step Functions, AWS Lambda, Application Load Balancers, Amazon EC2, Amazon RDS (MySQL), and the AWS Database Migration Service, and Route53.

(Sorry, couldn’t find youtube / slides 😦 )

ARC335 – Failing Successfully in the Cloud: AWS Approach to Resilient Design

AWS global infrastructure provides the tools customers need to design resilient and reliable services. In this session, we discuss how to get the most out of these tools.

(Sorry, couldn’t find youtube / slides 😦 )

SRV305 – Inside AWS: Technology Choices for Modern Applications

AWS offers a wide range of cloud computing services and technologies, but we rarely give opinions about which services and technologies customers should choose. When it comes to building our own services, our engineering groups have strong opinions, and they express them in the technologies they pick. Join Tim Bray, senior principal engineer, to hear about the high-level choices that developers at AWS and our customers have to make. Here are a few: Are microservices always the best choice? Serverless, containers, or serverless containers? Is relational over? Is Java over? The talk is technical and based on our experience in building AWS services and working with customers on their cloud-native apps.

Couldn’t find slides, but someone blogged about it here