Tencent Cloud SCF - Serverless Functions That Actually Work

Been running this since March 2024 in production. After switching from AWS Lambda, here's what actually matters when you're dealing with Tencent's serverless platform.

The real advantage isn't just the lower costs - it's that SCF works better for Asian traffic patterns and plays nice with Tencent's other services if you're already stuck in their ecosystem.

The Good Stuff

Performance and Regional Advantages

Python and Node.js work fine. Java is supported but cold starts are brutal - we're talking 3-5 seconds on a bad day. Go runtime is fast but the tooling feels half-baked compared to AWS.

The Asian regions are solid - I've had good luck with Hong Kong and Singapore. If you're serving users in China, this is probably your best bet since AWS Lambda has connectivity issues there.

Pricing is decent. We switched from Lambda and I think we're saving money, but hard to tell exactly since our usage changed too. The Asian regions are definitely cheaper and our traffic patterns fit their free tier better.

The Pain Points

Documentation quality is all over the place. The Python guides are decent, but try finding good examples for Go integration with their message queues - good luck with that.

Error messages are often useless. "Function execution failed" doesn't help when you're troubleshooting during dinner. The logs are better than they used to be, but still not great compared to CloudWatch.

VPC setup took me a weekend to figure out the first time. The console UI is functional but feels like it was designed by committee. Everything works, but it's not intuitive. Also, if your subnet name has underscores, the VPC wizard just fails silently in step 3.

Language Support Status

Python: Works great. Python 2.7 is dead - use Python 3, whatever version is current. Most libraries work fine, but anything that needs compiled extensions can be tricky.

Node.js: Solid choice. They support modern versions now but documentation sometimes has old examples that don't work anymore.

Java: Technically works. Cold starts are painful. If you're doing Java, you probably want Lambda instead unless you're locked into Tencent's ecosystem.

Go: Fast when it works. Limited examples and community support. Good for high-performance stuff but expect to figure things out yourself.

Deployment Reality

The web console editor is fine for quick prototypes but anything real needs proper CI/CD. ZIP upload works but gets annoying fast.

I ended up using their Serverless Framework plugin for production deployments. It's not as polished as AWS's tooling but does the job once you get it configured.

Pro tip: Test your deployment packages locally first. The runtime environment sometimes has different library versions than what the docs claim.

OK, here's the stuff they don't tell you in the docs. After 6 months in production, I've learned there are deeper performance and cost considerations that the documentation glosses over.

Marketing says SCF scales instantly, never fails, and requires zero effort. Bullshit. After running SCF in production with real traffic and real money on the line, here's what actually happens.

This isn't just theory or toy examples. These are the performance numbers, cost breakdowns, and painful lessons learned from production deployments serving actual users.

Scaling and Performance

Automatic Scaling and Resource Management

SCF scales OK. Marketing says 'instant' but it's more like 'fast enough to not hate your life.' I've watched it go from 10 to 1000 concurrent functions without dying, which is more than I can say for some other platforms.

Cold starts are the usual serverless pain point:

Performance breakdown by runtime:

• Python: Usually pretty fast, maybe 500ms? Pandas makes it way worse though
• Node.js: Usually 300-600ms, depends what you import
• Java: Takes forever, sometimes 3+ seconds
• Go: Fastest option but still not instant

Lambda usually starts faster, but SCF isn't bad. If you're serving Asian users, the regional advantage makes up for it.

Memory allocation directly affects your bill. The default 128MB runs out fast if you're doing anything beyond "hello world." I usually start with 512MB for anything real.

You can set concurrency limits per function, which is useful to prevent runaway costs when things go sideways. I learned this the hard way when a bug caused infinite recursion and AWS bill was stupid expensive - I don't remember exactly but it was way more than expected.

Triggers That Actually Matter

Event-Driven Architecture in Action

COS triggers: Work great for file processing. Set it up once and forget about it. Perfect for image resizing, log processing, that kind of thing.

API Gateway: Does the job but the routing config is confusing at first. Custom domains take forever to propagate - plan for 30-60 minutes, not the "5 minutes" the docs claim.

Timer triggers: Cron jobs basically. Reliable but limited compared to AWS EventBridge. You can't do complex schedules like "first Monday of every month."

CMQ: Message queue integration. Works but documentation is sparse. Debugging failed message processing is a nightmare because error handling is weird.

What Breaks

Execution time limit is something like 15 minutes (I think - check the current docs). Sounds like a lot until you hit it processing a large file. We had to break our PDF generation into chunks because single-threaded processing kept timing out.

VPC functions take longer to cold start and cost more. Only use if you actually need private network access. I spent weeks optimizing VPC performance before realizing I didn't even need it.

Outbound data transfer adds up fast if you're calling external APIs. The free tier doesn't include data transfer, and those costs can surprise you.

Security and IAM Gotchas

Security and Access Control

IAM setup is powerful but complex. The learning curve is steep if you're coming from simpler platforms. Permissions are granular but debugging access issues is time-consuming.

Function isolation works well, but debugging cross-function communication is harder than it should be. The error messages don't tell you if it's a permissions issue or a networking problem.

Integration Reality

Database connections: Work fine but connection pooling is tricky. Each function instance manages its own connections, so you can exhaust your DB connection pool under load.

COS integration: Solid and fast within the same region. Cross-region transfers are slow and expensive.

API Gateway: Functional but feature-poor compared to AWS. Custom authorizers are limited and documentation is lacking.

Production War Stories

Been using this in production since March 2024. Here's what I've learned:

The monitoring tools are shit. Finding specific errors in the logs is like searching for a needle in a haystack. The console search functionality is complete garbage.

Deployment rollbacks aren't automated. If you push broken code, you're manually rolling back. Plan your deployment strategy accordingly.

Regional differences matter. Hong Kong and Singapore perform well for international traffic. Mumbai and other newer regions have occasional reliability issues.

Version management is primitive compared to Lambda. No blue-green deployments out of the box. You'll need to build your own canary deployment system if you want zero-downtime releases.

The free tier runs out faster than you think. 400,000 GB-seconds sounds generous until you factor in memory allocation. A 1GB function uses 8x more "GB-seconds" than a 128MB function.

The Production Reality Summary

Here's what I've learned: SCF works, but it's not magic. You'll spend time optimizing memory allocation, fighting with VPC cold starts, and deciphering cryptic error messages. The cost savings are real, especially for Asian traffic, but you pay for them with increased complexity and limited tooling.

SCF isn't perfect, but the trade-offs make sense for Asian deployments and cost-sensitive apps. Just know what you're getting into before you commit.