## Problem
This is mainly to limit our concurrency, rather than to speed up
requests (I was doing some sanity checks on performance of the service
with thousands of shards)
## Summary of changes
- Enable the `diesel:r2d2` feature, which provides an async connection
pool
- Acquire a connection before entering spawn_blocking for a database
transaction (recall that diesel's interface is sync)
- Set a connection pool size of 99 to fit within default postgres limit
(100)
- Also set the tokio blocking thread count to accomodate the same number
of blocking tasks (the only thing we use spawn_blocking for is database
calls).
## Problem
Running some memory profiling with high concurrent request rate shows
seemingly some memory fragmentation.
## Summary of changes
Eventually, we will want to separate global memory (caches) from local
memory (per connection handshake and per passthrough).
Using a string interner for project info cache helps reduce some of the
fragmentation of the global cache by having a single heap dedicated to
project strings, and not scattering them throughout all a requests.
At the same time, the interned key is 4 bytes vs the 24 bytes that
`SmolStr` offers.
Important: we should only store verified strings in the interner because
there's no way to remove them afterwards. Good for caching responses
from console.
## Problem
Passing secrets in via CLI/environment is awkward when using helm for
deployment, and not ideal for security (secrets may show up in ps,
/proc).
We can bypass these issues by simply connecting directly to the AWS
Secrets Manager service at runtime.
## Summary of changes
- Add dependency on aws-sdk-secretsmanager
- Update other aws dependencies to latest, to match transitive
dependency versions
- Add `Secrets` type in attachment service, using AWS SDK to load if
secrets are not provided on the command line.
## Problem
Measuring cardinality using logs is expensive and slow.
## Summary of changes
Implement a pre-aggregated HyperLogLog-based cardinality estimate.
HyperLogLog estimates the cardinality of a set by using the probability
that the uniform hash of a value will have a run of n 0s at the end is
`1/2^n`, therefore, having observed a run of `n` 0s suggests we have
measured `2^n` distinct values. By using multiple shards, we can use the
harmonic mean to get a more accurate estimate.
We record this into a Prometheus time-series. HyperLogLog counts can be
merged by taking the `max` of each shard. We can apply a `max_over_time`
in order to find the estimate of cardinality of distinct values over
time
## Problem
Spun off from https://github.com/neondatabase/neon/pull/6394 -- this PR
is just the persistence parts and the changes that enable it to work
nicely
## Summary of changes
- Revert #6444 and #6450
- In neon_local, start a vanilla postgres instance for the attachment
service to use.
- Adopt `diesel` crate for database access in attachment service. This
uses raw SQL migrations as the source of truth for the schema, so it's a
soft dependency: we can switch libraries pretty easily.
- Rewrite persistence.rs to use postgres (via diesel) instead of JSON.
- Preserve JSON read+write at startup and shutdown: this enables using
the JSON format in compatibility tests, so that we don't have to commit
to our DB schema yet.
- In neon_local, run database creation + migrations before starting
attachment service
- Run the initial reconciliation in Service::spawn in the background, so
that the pageserver + attachment service don't get stuck waiting for
each other to start, when restarting both together in a test.
## Summary of changes
### RequestMonitoring
We want to add an event stream with information on each request for
easier analysis than what we can do with diagnostic logs alone
(https://github.com/neondatabase/cloud/issues/8807). This
RequestMonitoring will keep a record of the final state of a request. On
drop it will be pushed into a queue to be uploaded.
Because this context is a bag of data, I don't want this information to
impact logic of request handling. I personally think that weakly typed
data (such as all these options) makes for spaghetti code. I will
however allow for this data to impact rate-limiting and blocking of
requests, as this does not _really_ change how a request is handled.
### Parquet
Each `RequestMonitoring` is flushed into a channel where it is converted
into `RequestData`, which is accumulated into parquet files. Each file
will have a certain number of rows per row group, and several row groups
will eventually fill up the file, which we then upload to S3.
We will also upload smaller files if they take too long to construct.
- add pgbouncer_settings section to compute spec;
- add pgbouncer-connstr option to compute_ctl.
- add pgbouncer-ini-path option to compute_ctl. Default: /etc/pgbouncer/pgbouncer.ini
Apply pgbouncer config on compute start and respec to override default spec.
Save pgbouncer config updates to pgbouncer.ini to preserve them across pgbouncer restarts.
## Problem
The cancellation code was confusing and error prone (as seen before in
our memory leaks).
## Summary of changes
* Use the new `TaskTracker` primitve instead of JoinSet to gracefully
wait for tasks to shutdown.
* Updated libs/utils/completion to use `TaskTracker`
* Remove `tokio::select` in favour of `futures::future::select` in a
specialised `run_until_cancelled()` helper function
There is double buffering in remote_storage and in pageserver for 8KiB
in using `tokio::io::copy` to read `BufReader<ReaderStream<_>>`.
Switches downloads and uploads to use `Stream<Item =
std::io::Result<Bytes>>`. Caller and only caller now handles setting up
buffering. For reading, `Stream<Item = ...>` is also a `AsyncBufRead`,
so when writing to a file, we now have `tokio::io::copy_buf` reading
full buffers and writing them to `tokio::io::BufWriter` which handles
the buffering before dispatching over to `tokio::fs::File`.
Additionally implements streaming uploads for azure. With azure
downloads are a bit nicer than before, but not much; instead of one huge
vec they just hold on to N allocations we got over the wire.
This PR will also make it trivial to switch reading and writing to
io-uring based methods.
Cc: #5563.
## Problem
See #2592
## Summary of changes
Compresses the results of initdb into a .tar.zst file and uploads them
to S3, to enable usage in recovery from lsn.
Generations should not be involved I think because we do this only once
at the very beginning of a timeline.
---------
Co-authored-by: Joonas Koivunen <joonas@neon.tech>
## Problem
A user can perform many database connections at the same instant of time
- these will all cache miss and materialise as requests to the control
plane. #5705
## Summary of changes
I am using a `DashMap` (a sharded `RwLock<HashMap>`) of endpoints ->
semaphores to apply a limiter. If the limiter is enabled (permits > 0),
the semaphore will be retrieved per endpoint and a permit will be
awaited before continuing to call the wake_compute endpoint.
### Important details
This dashmap would grow uncontrollably without maintenance. It's not a
cache so I don't think an LRU-based reclamation makes sense. Instead,
I've made use of the sharding functionality of DashMap to lock a single
shard and clear out unused semaphores periodically.
I ran a test in release, using 128 tokio tasks among 12 threads each
pushing 1000 entries into the map per second, clearing a shard every 2
seconds (64 second epoch with 32 shards). The endpoint names were
sampled from a gamma distribution to make sure some overlap would occur,
and each permit was held for 1ms. The histogram for time to clear each
shard settled between 256-512us without any variance in my testing.
Holding a lock for under a millisecond for 1 of the shards does not
concern me as blocking
## Problem
Transactions break connections in the pool
fixes#4698
## Summary of changes
* Pool `Client`s are smart object that return themselves to the pool
* Pool `Client`s can be 'discard'ed
* Pool `Client`s are discarded when certain errors are encountered.
* Pool `Client`s are discarded when ReadyForQuery returns a non-idle
state.
Adds prototype-level support for [Azure blob storage](https://azure.microsoft.com/en-us/products/storage/blobs). Some corners were cut, see the TODOs and the followup issue #5567 for details.
Steps to try it out:
* Create a storage account with block blobs (this is a per-storage
account setting).
* Create a container inside that storage account.
* Set the appropriate env vars: `AZURE_STORAGE_ACCOUNT,
AZURE_STORAGE_ACCESS_KEY, REMOTE_STORAGE_AZURE_CONTAINER,
REMOTE_STORAGE_AZURE_REGION`
* Set the env var `ENABLE_REAL_AZURE_REMOTE_STORAGE=y` and run `cargo
test -p remote_storage azure`
Fixes #5562
## Problem
The S3 scrubber currently lives at
https://github.com/neondatabase/s3-scrubber
We don't have tests that use it, and it has copies of some data
structures that can get stale.
## Summary of changes
- Import the s3-scrubber as `s3_scrubber/
- Replace copied_definitions/ in the scrubber with direct access to the
`utils` and `pageserver` crates
- Modify visibility of a few definitions in `pageserver` to allow the
scrubber to use them
- Update scrubber code for recent changes to `IndexPart`
- Update `KNOWN_VERSIONS` for IndexPart and move the definition into
index.rs so that it is easier to keep up to date
As a future refinement, it would be good to pull the remote persistence
types (like IndexPart) out of `pageserver` into a separate library so
that the scrubber doesn't have to link against the whole pageserver, and
so that it's clearer which types need to be public.
Co-authored-by: Kirill Bulatov <kirill@neon.tech>
Co-authored-by: Dmitry Rodionov <dmitry@neon.tech>
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
## Problem
The `EphemeralFile::write_blob` function accesses the page cache
internally. We want to require `async` for these accesses in #5023.
## Summary of changes
This removes the implementaiton of the `BlobWriter` trait for
`EphemeralFile` and turns the `write_blob` function into an inherent
function. We can then make it async as well as the `push_bytes`
function. We move the `SER_BUFFER` thread-local into the
`InMemoryLayerInner` so that the same buffer can be accessed by
different threads as the async is (potentially) moved between threads.
Part of #4743, preparation for #5023.
Add infrastructure to dynamically load postgres extensions and shared libraries from remote extension storage.
Before postgres start downloads list of available remote extensions and libraries, and also downloads 'shared_preload_libraries'. After postgres is running, 'compute_ctl' listens for HTTP requests to load files.
Postgres has new GUC 'extension_server_port' to specify port on which 'compute_ctl' listens for requests.
When PostgreSQL requests a file, 'compute_ctl' downloads it.
See more details about feature design and remote extension storage layout in docs/rfcs/024-extension-loading.md
---------
Co-authored-by: Anastasia Lubennikova <anastasia@neon.tech>
Co-authored-by: Alek Westover <alek.westover@gmail.com>
Adds in a barrier for the duration of the `Tenant::shutdown`.
`pageserver_shutdown` will join this await, `detach`es and `ignore`s
will not.
Fixes#4429.
---------
Co-authored-by: Christian Schwarz <christian@neon.tech>
Allure does not support ansi colored logs, yet `compute_ctl` has them.
Upgrade criterion to get rid of atty dependency, disable ansi colors,
remove atty dependency and disable ansi feature of tracing-subscriber.
This is a heavy-handed approach. I am not aware of a workflow where
you'd want to connect a terminal directly to for example `compute_ctl`,
usually you find the logs in a file. If someone had been using colors,
they will now need to:
- turn the `tracing-subscriber.default-features` to `true`
- edit their wanted project to have colors
I decided to explicitly disable ansi colors in case we would have in
future a dependency accidentally enabling the feature on
`tracing-subscriber`, which would be quite surprising but not
unimagineable.
By getting rid of `atty` from dependencies we get rid of
<https://github.com/advisories/GHSA-g98v-hv3f-hcfr>.
See https://github.com/neondatabase/neon/pull/3991
Brings the changes back with the right way to use new `toml_edit` to
deserialize values and a unit test for this.
All non-trivial updates extracted into separate commits, also `carho hakari` data and its manifest format were updated.
3 sets of crates remain unupdated:
* `base64` — touches proxy in a lot of places and changed its api (by 0.21 version) quite strongly since our version (0.13).
* `opentelemetry` and `opentelemetry-*` crates
```
error[E0308]: mismatched types
--> libs/tracing-utils/src/http.rs:65:21
|
65 | span.set_parent(parent_ctx);
| ---------- ^^^^^^^^^^ expected struct `opentelemetry_api::context::Context`, found struct `opentelemetry::Context`
| |
| arguments to this method are incorrect
|
= note: struct `opentelemetry::Context` and struct `opentelemetry_api::context::Context` have similar names, but are actually distinct types
note: struct `opentelemetry::Context` is defined in crate `opentelemetry_api`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/opentelemetry_api-0.19.0/src/context.rs:77:1
|
77 | pub struct Context {
| ^^^^^^^^^^^^^^^^^^
note: struct `opentelemetry_api::context::Context` is defined in crate `opentelemetry_api`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/opentelemetry_api-0.18.0/src/context.rs:77:1
|
77 | pub struct Context {
| ^^^^^^^^^^^^^^^^^^
= note: perhaps two different versions of crate `opentelemetry_api` are being used?
note: associated function defined here
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-opentelemetry-0.18.0/src/span_ext.rs:43:8
|
43 | fn set_parent(&self, cx: Context);
| ^^^^^^^^^^
For more information about this error, try `rustc --explain E0308`.
error: could not compile `tracing-utils` due to previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `tracing-utils` due to previous error
```
`tracing-opentelemetry` of version `0.19` is not yet released, that is supposed to have the update we need.
* similarly, `rustls`, `tokio-rustls`, `rustls-*` and `tls-listener` crates have similar issue:
```
error[E0308]: mismatched types
--> libs/postgres_backend/tests/simple_select.rs:112:78
|
112 | let mut make_tls_connect = tokio_postgres_rustls::MakeRustlsConnect::new(client_cfg);
| --------------------------------------------- ^^^^^^^^^^ expected struct `rustls::client::client_conn::ClientConfig`, found struct `ClientConfig`
| |
| arguments to this function are incorrect
|
= note: struct `ClientConfig` and struct `rustls::client::client_conn::ClientConfig` have similar names, but are actually distinct types
note: struct `ClientConfig` is defined in crate `rustls`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/rustls-0.21.0/src/client/client_conn.rs:125:1
|
125 | pub struct ClientConfig {
| ^^^^^^^^^^^^^^^^^^^^^^^
note: struct `rustls::client::client_conn::ClientConfig` is defined in crate `rustls`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/rustls-0.20.8/src/client/client_conn.rs:91:1
|
91 | pub struct ClientConfig {
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: perhaps two different versions of crate `rustls` are being used?
note: associated function defined here
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-postgres-rustls-0.9.0/src/lib.rs:23:12
|
23 | pub fn new(config: ClientConfig) -> Self {
| ^^^
For more information about this error, try `rustc --explain E0308`.
error: could not compile `postgres_backend` due to previous error
warning: build failed, waiting for other jobs to finish...
```
* aws crates: I could not make new API to work with bucket endpoint overload, and console e2e tests failed.
Other our tests passed, further investigation is worth to be done in https://github.com/neondatabase/neon/issues/4008
All non-trivial updates extracted into separate commits, also `carho
hakari` data and its manifest format were updated.
3 sets of crates remain unupdated:
* `base64` — touches proxy in a lot of places and changed its api (by
0.21 version) quite strongly since our version (0.13).
* `opentelemetry` and `opentelemetry-*` crates
```
error[E0308]: mismatched types
--> libs/tracing-utils/src/http.rs:65:21
|
65 | span.set_parent(parent_ctx);
| ---------- ^^^^^^^^^^ expected struct `opentelemetry_api::context::Context`, found struct `opentelemetry::Context`
| |
| arguments to this method are incorrect
|
= note: struct `opentelemetry::Context` and struct `opentelemetry_api::context::Context` have similar names, but are actually distinct types
note: struct `opentelemetry::Context` is defined in crate `opentelemetry_api`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/opentelemetry_api-0.19.0/src/context.rs:77:1
|
77 | pub struct Context {
| ^^^^^^^^^^^^^^^^^^
note: struct `opentelemetry_api::context::Context` is defined in crate `opentelemetry_api`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/opentelemetry_api-0.18.0/src/context.rs:77:1
|
77 | pub struct Context {
| ^^^^^^^^^^^^^^^^^^
= note: perhaps two different versions of crate `opentelemetry_api` are being used?
note: associated function defined here
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-opentelemetry-0.18.0/src/span_ext.rs:43:8
|
43 | fn set_parent(&self, cx: Context);
| ^^^^^^^^^^
For more information about this error, try `rustc --explain E0308`.
error: could not compile `tracing-utils` due to previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `tracing-utils` due to previous error
```
`tracing-opentelemetry` of version `0.19` is not yet released, that is
supposed to have the update we need.
* similarly, `rustls`, `tokio-rustls`, `rustls-*` and `tls-listener`
crates have similar issue:
```
error[E0308]: mismatched types
--> libs/postgres_backend/tests/simple_select.rs:112:78
|
112 | let mut make_tls_connect = tokio_postgres_rustls::MakeRustlsConnect::new(client_cfg);
| --------------------------------------------- ^^^^^^^^^^ expected struct `rustls::client::client_conn::ClientConfig`, found struct `ClientConfig`
| |
| arguments to this function are incorrect
|
= note: struct `ClientConfig` and struct `rustls::client::client_conn::ClientConfig` have similar names, but are actually distinct types
note: struct `ClientConfig` is defined in crate `rustls`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/rustls-0.21.0/src/client/client_conn.rs:125:1
|
125 | pub struct ClientConfig {
| ^^^^^^^^^^^^^^^^^^^^^^^
note: struct `rustls::client::client_conn::ClientConfig` is defined in crate `rustls`
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/rustls-0.20.8/src/client/client_conn.rs:91:1
|
91 | pub struct ClientConfig {
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: perhaps two different versions of crate `rustls` are being used?
note: associated function defined here
--> /Users/someonetoignore/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-postgres-rustls-0.9.0/src/lib.rs:23:12
|
23 | pub fn new(config: ClientConfig) -> Self {
| ^^^
For more information about this error, try `rustc --explain E0308`.
error: could not compile `postgres_backend` due to previous error
warning: build failed, waiting for other jobs to finish...
```
* aws crates: I could not make new API to work with bucket endpoint
overload, and console e2e tests failed.
Other our tests passed, further investigation is worth to be done in
https://github.com/neondatabase/neon/issues/4008
- Add support for splitting async postgres_backend into read and write halfes.
Safekeeper needs this for bidirectional streams. To this end, encapsulate
reading-writing postgres messages to framed.rs with split support without any
additional changes (relying on BufRead for reading and BytesMut out buffer for
writing).
- Use async postgres_backend throughout safekeeper (and in proxy auth link
part).
- In both safekeeper COPY streams, do read-write from the same thread/task with
select! for easier error handling.
- Tidy up finishing CopyBoth streams in safekeeper sending and receiving WAL
-- join split parts back catching errors from them before returning.
Initially I hoped to do that read-write without split at all, through polling
IO:
https://github.com/neondatabase/neon/pull/3522
However that turned out to be more complicated than I initially expected
due to 1) borrow checking and 2) anon Future types. 1) required Rc<Refcell<...>>
which is Send construct just to satisfy the checker; 2) can be workaround with
transmute. But this is so messy that I decided to leave split.
## Describe your changes
## Issue ticket number and link
#3479
## Checklist before requesting a review
- [x] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.
On the surface, this doesn't add much, but there are some benefits:
* We can do graceful shutdowns and thus record more code coverage data.
* We now have a foundation for the more interesting behaviors, e.g. "stop
accepting new connections after SIGTERM but keep serving the existing ones".
* We give the otel machinery a chance to flush trace events before
finally shutting down.
This commit sets up OpenTelemetry tracing and exporter, so that they
can be exported as OpenTelemetry traces as well.
All outgoing HTTP requests will be traced. A separate (child)
span is created for each outgoing HTTP request, and the tracing
context is also propagated to the server in the HTTP headers.
If tracing is enabled in the control plane and compute node too, you
can now get an end-to-end distributed trace of what happens when a new
connection is established, starting from the handshake with the
client, creating the 'start_compute' operation in the control plane,
starting the compute node, all the way to down to fetching the base
backup and the availability checks in compute_ctl.
Co-authored-by: Dmitry Ivanov <dima@neon.tech>
This patch adds a timed LRU cache implementation and a compute node info cache on top of that.
Cache entries might expire on their own (default ttl=5mins) or become invalid due to real-world events,
e.g. compute node scale-to-zero event, so we add a connection retry loop with a wake-up call.
Solved problems:
- [x] Find a decent LRU implementation.
- [x] Implement timed LRU on top of that.
- [x] Cache results of `proxy_wake_compute` API call.
- [x] Don't invalidate newer cache entries for the same key.
- [x] Add cmdline configuration knobs (requires some refactoring).
- [x] Add failed connection estab metric.
- [x] Refactor auth backends to make things simpler (retries, cache
placement, etc).
- [x] Address review comments (add code comments + cleanup).
- [x] Retry `/proxy_wake_compute` if we couldn't connect to a compute
(e.g. stalled cache entry).
- [x] Add high-level description for `TimedLru`.
TODOs (will be addressed later):
- [ ] Add cache metrics (hit, spurious hit, miss).
- [ ] Synchronize http requests across concurrent per-client tasks
(https://github.com/neondatabase/neon/pull/3331#issuecomment-1399216069).
- [ ] Cache results of `proxy_get_role_secret` API call.
This allows tracing the startup actions e.g. with Jaeger
(https://www.jaegertracing.io/). We use the "tracing-opentelemetry"
crate, which turns tracing spans into OpenTelemetry spans, so you can
use the usual "#[instrument]" directives to add tracing.
I put the tracing initialization code to a separate crate,
`tracing-utils`, so that we can reuse it in other programs. We
probably want to set up tracing in the same way in all our programs.
Co-authored-by: Joonas Koivunen <joonas@neon.tech>
Refactors Compute::prepare_and_run. It's split into subroutines
differently, to make it easier to attach tracing spans to the
different stages. The high-level logic for waiting for Postgres to
exit is moved to the caller.
Replace 'env_logger' with 'tracing', and add `#instrument` directives
to different stages fo the startup process. This is a fairly
mechanical change, except for the changes in 'spec.rs'. 'spec.rs'
contained some complicated formatting, where parts of log messages
were printed directly to stdout with `print`s. That was a bit messed
up because the log normally goes to stderr, but those lines were
printed to stdout. In our docker images, stderr and stdout both go to
the same place so you wouldn't notice, but I don't think it was
intentional.
This changes the log format to the default
'tracing_subscriber::format' format. It's different from the Postgres
log format, however, and because both compute_tools and Postgres print
to the same log, it's now a mix of two different formats. I'm not
sure how the Grafana log parsing pipeline can handle that. If it's a
problem, we can build custom formatter to change the compute_tools log
format to be the same as Postgres's, like it was before this commit,
or we can change the Postgres log format to match tracing_formatter's,
or we can start printing compute_tool's log output to a different
destination than Postgres
It was nice to have and useful at the time, but unfortunately the method
used to gather the profiling data doesn't play nicely with 'async'. PR
#3228 will turn 'get_page_at_lsn' function async, which will break the
profiling support. Let's remove it, and re-introduce some kind of
profiling later, using some different method, if we feel like we need it
again.
I looked at "cargo tree" output and noticed that through various
dependencies, we are depending on both native-tls and rustls. We have
tried to standardize on rustls for everything, but dependencies on
native-tls have crept in recently. One such dependency came from
'reqwest' with default features in pageserver, used for
consumption_metrics. Another dependency was from 'sentry'. Both
'reqwest' and 'sentry' use native-tls by default, but can use 'rustls'
if compiled with the right feature flags.
Add new background job to collect billing metrics for each tenant and
send them to the HTTP endpoint.
Metrics are cached, so we don't send non-changed metrics.
Add metric collection config parameters:
metric_collection_endpoint (default None, i.e. disabled)
metric_collection_interval (default 60s)
Add test_metric_collection.py to test metric collection
and sending to the mocked HTTP endpoint.
Use port distributor in metric_collection test
review fixes: only update cache after metrics were send successfully, simplify code
disable metric collection if metric_collection_endpoint is not provided in config
