AWS SQS Error: FIFO '.fifo' Naming and Deduplication Traps (Messages Rejected, Ignored, or Duplicated)

#aws#sqs#lambda#cloud

If you respect the .fifo suffix, set MessageGroupId correctly, and understand deduplication behavior, FIFO works exactly as advertised.

Problem

You create an Amazon SQS FIFO queue and immediately run into one or more of the following:

• Messages fail to send with vague or confusing errors
• Messages are silently deduplicated when you expect them to be processed
• Messages are processed out of order despite using FIFO
• Your producer “works” with a standard queue but fails with FIFO

Nothing in your code looks wrong, yet FIFO behaves nothing like you expected.

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Clarifying the Issue

FIFO queues are strict by design. They enforce rules that standard queues do not.

Most FIFO failures are not bugs—they are contract violations.

In practice, problems almost always come down to three requirements that FIFO enforces rigidly:

1. The queue name must end with .fifo
2. Every message must include a MessageGroupId
3. Deduplication behavior must be explicitly understood

If you miss any one of these, FIFO will either reject your messages or behave in ways that feel unpredictable.

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Why It Matters

FIFO queues are typically chosen for correctness, not throughput:

• Financial transactions
• Ordered workflows
• State transitions
• Exactly-once effects (not delivery)

When FIFO is misconfigured, the failure modes are dangerous:

• Messages appear to “vanish” due to deduplication
• Throughput collapses because all messages share one group
• Ordering guarantees silently disappear
• Systems behave worse than standard queues

FIFO is powerful—but only if you play by its rules.

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Key Terms

• FIFO Queue – A queue that preserves order and supports deduplication
• .fifo Suffix – Required naming convention for FIFO queues
• MessageGroupId – Groups messages for ordered processing
• MessageDeduplicationId – Identifier used to deduplicate messages
• Content-Based Deduplication – Hash-based automatic deduplication

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Steps at a Glance

1. Confirm the queue name ends with .fifo
2. Ensure every message includes a MessageGroupId
3. Understand how FIFO ordering actually works
4. Fix deduplication assumptions
5. Validate throughput expectations

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Detailed Steps

Step 1: Verify the .fifo Suffix

This is non-negotiable.

If your queue name does not end with .fifo, it is not a FIFO queue—regardless of how it was created or described.

Examples:

• ✅ orders-processing.fifo
• ❌ orders-processing

Action

• Check the queue name, not just the console label
• Update producers to point to the correct FIFO queue URL
• Do not assume renaming is cosmetic—it changes queue type

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Step 2: Ensure Every Message Has a MessageGroupId

FIFO queues require a MessageGroupId for every message.

Without it:

• Messages are rejected
• Or libraries fail silently

Critical behavior

• Ordering is guaranteed within a group
• Ordering is not guaranteed across groups

Action

• Always set MessageGroupId
• Do not hard-code a single group unless ordering truly must be global

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Step 3: Understand the Ordering Trap

A common mistake:

❌ “FIFO means one message at a time.”

That is false.

FIFO means:

• Messages in the same group are processed in order
• Different groups are processed in parallel

If all messages use the same MessageGroupId:

• Throughput drops to near zero
• The queue becomes effectively single-threaded

Action

• Choose group IDs that preserve correctness without killing throughput
• Think in terms of ordering domains, not global order

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Step 4: Fix Deduplication Assumptions

FIFO deduplication operates on a 5-minute window.

You have two options:

Option A: Explicit Deduplication

• You provide MessageDeduplicationId
• Messages with the same ID within 5 minutes are dropped

Option B: Content-Based Deduplication

• SQS hashes the message body
• Identical payloads are deduplicated automatically

The Trap

• Replaying the same payload for retries or tests
• Expecting FIFO to “try again”
• FIFO drops it instead

Action

• Be explicit about deduplication strategy
• Do not reuse deduplication IDs accidentally
• Understand that deduplication is working as designed

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Step 5: Validate Throughput Expectations

FIFO queues trade throughput for guarantees.

Limits to remember:

• Ordering reduces parallelism
• Message groups control concurrency
• FIFO is slower than standard by design

Action

• Do not migrate to FIFO for convenience
• Use FIFO only where ordering or deduplication is truly required
• Measure before and after

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Pro Tips

• FIFO is about correctness, not speed
• Multiple MessageGroupIds restore parallelism
• Deduplication can hide bugs during testing
• Standard queues are often the right default
• FIFO should be a conscious, documented choice

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Conclusion

FIFO queues are not “standard queues with extra features.”

They are a different contract.

If you respect the .fifo suffix, set MessageGroupId correctly, and understand deduplication behavior, FIFO works exactly as advertised.

If you don’t, it will reject, drop, or serialize your messages—silently and correctly.

FIFO is strict because correctness is strict. This Fix-It helps you stay on the right side of that line.

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Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.